As @Bessemer says, I too think BFG:XR is well-balanced compared with previous iterations, and very complete, except perhaps for the final balancing on the Tyranids (I think Xca|iber got the Orks sorted before the end). I think restricting the Proteus is probably the easiest fix there (though there’s some discussion above).
For the timeline of BFG ‘editions’, this reply from @Horizon and the thread he linked to are useful if you haven’t seen them yet:
http://www.forum.specialist-arms.com/index.php?topic=8631.0Lots of revision efforts have happened over the years, both when GW still actively maintained the game, and when that task fell to the various BFG communities. BFG:R was one of those attempts that aimed to really engage the community in improving and polishing the BFG Armada + FAQ2010 rules (along with some additions over the years from particularly excellent community rules).
BFG:XR uses BFG:R as a base, and aimed to complete it (and you can read about Xca|iber’s strategies in this thread, of course). It clarifies lots of small things and changes some of the odd things that didn’t really make sense, and compiles everything (except the unfinished campaign rules) into an edition all with one date (instead of bits and pieces of things with different levels of revision). BFG:XR consequently makes many fleet lists more complete. In my humble opinion, BFG:XR is the best complete revision of BFG to date.
So, if you’d like to use the last, most ‘official’ GW production, BFG + Armada + FAQ2010 is the one to use, and the most widely accepted (having said that, there’s always a little controversy).
However, as is typical of Games Workshop, those may not be the most well-constructed version of the rules; BFG:XR is probably the best at that, that I know of. There are not significant enough core rule changes between the two for most people to really notice, though, except that the community-created Eldar Move-Move-Shoot rules are included in BFG:XR rather than the original Move-Shoot-Move rules (the opinion of many on these forums, at least, is that the ‘MMS’ rules work better). Hopefully someone has the campaign rules, but you could easily use the original BFG campaign rules with BFG:XR.
Of course, there’s nothing stopping you from trying out one combination of rules, and then deciding as a group to use something from another revision—an example might be that the original BFG Retribution and Emperor class battleship weapons stats/points values are a bit dodgy; or maybe you like the BFG:XR Orks but prefer the original MSM Eldar. And it’s totally fine to want to stick with the most ‘official’ rules out there, but the BFG community these days has no official support and is generally just local groups, so there’s perhaps less reason to other than personal preference.
Hopefully our thoughts have been helpful!
Edit: As to someone picking up the mantle, the only person who’s really posted on here about doing something like that is Green_Squad_Leader—though he was mentioning creating a new revision (see above).
I think BFG:XR (except for the aforementioned tweaks to Tyranids, and the missing campaign rules) is complete as it is. There will almost certainly be small things picked up on and suggested fixes from the community, but they’d just be small notes, I think. People are also always creating new fan ship designs and scenarios, which are easy to incorporate into games. Someone might try getting in touch with Xca|iber for the source document files, but not having those is an obstacle to further work on BFG:XR.
For the future of revisions overall, I personally reckon the most fruitful things to do would be getting BFG:XR more widely used, and working on more substantial revisions to the core BFG rules, like GSL is suggesting—the rules engine is pretty excellent, but it’d be interesting to see some modern rules innovations incorporated.
There is also the spectre of Games Workshop releasing a new Horus Heresy ‘BFG’ game, like they’re re-released Adeptus Titanicus—hopefully it’ll happen, hopefully it’ll be well-designed! But until we see it, it throws a lot of uncertainty out there for people wanting to revise BFG. The new version of the computerised BFG Armada could be interesting, too, though I think the BFG community has seen little to incorporate back into the tabletop game (except I reckon the long-range bombs would be a useful thing to implement).
