While I have little interest in how this will affect other armies (being biased), I can see this being a game changer for the Eldar. Whilst our current Codex covers most variations of the primary Craftworlds, it doesn't cover them to the degree we probably would like. When the Iyanden supplement dropped, it gave Eldar fans a taste of what could be expected in the future.
Let's break it down a bit though, into the pro's and con's. First, the positive aspects. In essence, the proposed rumors indicate the various flavors of Craftworlds out there will now have full "unbound" potential to be realised. Reminiscent of Codex: Craftworld Eldar, released as a supplement to the 3rd Edition Codex, how you wish to play will be purely your choice. I could almost hear my Biel Tan friends wet themselves with the force of a firehose.
Of course, this all depends on what will count as scoring. Pre-3rd edition, I never had a single Dire Avenger - they were just too plain and Guardian like for my tastes. Then along came the 4th Edition Codex which changed all of that. Now, however, I can do without them and return to a playstyle more fitting to a list I ran back in 2006, pre 4th Edition Codex Eldar. Want to include Warp Spiders, Striking Scorpions, Fire Dragons, Swooping Hawks, Dark Reapers etc and still have room for support vehicles? Well supposedly now you can.
So with the positives, let's also look at the middle ground and what the past has taught us. Whilst I recognise the tournament scene in the US is very different from that here in Australia, we (down under) have typically used comp systems to see people bring balanced armies and attitudes to the tabletop. My last tournament was in 2006, when the FOC was reinforced with percentage house rules in a bid to eliminate min/max/spam lists. Generally, for some years the rule was you must have 40%+ Troops and no more than 25% in any other section, plus you lost points for min/max units (except of course if you had one area completely empty - ie: no Elites, yet slightly more than 30% Fast Attack or Heavy Support). The two worked very well in tandem, and its still something I remain aware of when building lists even today.
As for the negatives? What I do see a lot of people complaining about is the potential to create broken lists - which I might add, already exist. Warhammer isn't a game designed on impeccable balance for the tournament scene, which is why Tournament Organisers (TOs) make house rules and the like to reinforce fair play that focuses more on Generalship than putting together an overpowered spam list, which proves nothing other than the person bringing it can identify such a unit... and spam it. Not exactly the sign of a brilliant tactician or strategist, nor will it win you any friends.
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"Panties in a twist" syndrome - aka symptoms of change
These days, Gamers are far to quick when jumping to negative conclusions. There have always been power gamers, but that doesn't mean you have to play against them. Take back some responsibility, stand up and say "No, that isn't in the spirit of the game". If every gamer did this, it would set about a resounding culture that would fix most of the niggles most commonly complained about. Stop complaining about the rules and how they're written, they will never be 100% ideal, instead, make the game work the way you want it to and enjoy it as such. Don't want to play against a spam list of Hell Turkeys? Refuse to play it, explain why and watch the behaviour change. In short, stop blaming the game and everything else surrounding it and be the change you want to see. It is really elementary stuff folks.
I believe a lot of the changes Games Workshop have made are to introduce flexibility, allowing us to do far more with what we have than was previously possible. The issue seems to be, we have so much flexibility that we're spoiled for choice given that previously, the 40k culture was so dumbed down and structured, no one really had to think for themselves. Now the chains are off, we can make it truly our own.
Given my profession in Governance and Change Management, I see this adversity to change on a daily basis - the funny thing about routine is people both love and hate it. They love it because life has already given us a lot to think about, so why add to that eh? The last part of that comment is the problem "Why add to it". Change is often perceived as "adding" to something previously observed as unbroken. Yet, why do we change? Because people are also curious creatures and get tired of routine, or things that take longer than one would like. So now you're probably asking "Ok big shot, so what would you propose to stop the complaining?". Pretty simple actually, Games Workshop would do well to produce an announcement something a little like this;
"We at Games Workshop appreciate your thoughts and comments as loyal customers. As such, we have listened to what you feel best reflect the common aspects surrounding your enjoyment of our products as part of the Hobby. Warhammer 40,000 7th Edition is a collaborative effort to both open up the game from its previously stale state to the wider gaming community to truly personalise your gaming experience whilst keeping in true spirit of the game - having fun. Change to the long standing army structure (Force Organisation Chart) allowing the new "Unbound" list design, giving players the opportunity to venture into new ways of playing with new and existing miniature investments. Games Workshop believes that by giving you more freedom of choice in how you play will help to grow your enjoyment of the game and in so doing, grow the company so we can continue to bring you high quality miniatures and products."
In the above, I have addressed the fact this isn't adding more weight but flexibility, explaining the benefits, showing this is the result of feedback from the gaming community in a bid to provide a richer experience for all.
TL;DR - To sum up...
Positive - Greater flexibility in Eldar lists, personalise your game and investment
Middle ground - Not a far cry from what has previously been indoctrinated in house rules
Negative - Increased capacity for making broken lists (the solution there is simple - take action rather than complaining about it, its the grown up thing to do).
Change - It isn't a bad thing, how it is delivered can make all the difference