I already have all the Birthright books, but I'd buy a new professionally produced version if it was published. It's not going to happen though, not enough potential sales to make it worth while publishing. It was even discussed by the birthright.net development team, but WotC is very restrictive on any of their worlds/settings, and it wasn't worth pursuing for any of the d20 publishers we spoke too. I believe that at the time the main sticking point was that WotC would have got to publish the core rulebook of the setting and then the d20 publisher would have got to publish any additional material, adventuers, accessories, etc. Obviously for most settings it is only the setting itself that sells in high volume, and BR never had the sales to make it worthwhile pursuing by anyone we had discussions with. However, you can always download the free version of the BRCS from birthright.net, and one day (If we ever find the time to actually sit down and write something), you may even see an updated 3.5 version of the rules.
Birthright could work with minitures for wars, but I've always felt that the heart of BR is the setting itself, not the domain rules, although that does add another level to the game. I don't, however, think that the UA bloodline system would transfer too well though, as it is primarily level-based. One of the things I've always liked about BR and it's bloodline system is that a relavitly low-level character (for example, Rogh Aglondier, a 3rd level wizard) can be as good a ruler as a high-level character simply because of the strength of his bloodline. Using the UA system for BR would take this away and again focus the game only on a person's level...
As much as I like BR, it is not, however, a system that transfers well to other world. It can work, but it is tied very much into the Bloodline rules. The BRCS (birthright.net's 3rd edition conversion) does more away from this somewhat. But in the end, if you have BR, why do you need other campaign settings??
By the way I'm currently running two Birthright games, one a campaign where my players are working together to forge a new kingdom, with one PC as regent, and the others and his lieutenants and allies. The other game is a adventure-based pbem that I've just started up that will be set in Aduria, the original home of Cerilia's human races.