It's early days, a deal as complex as the one that has just been agreed is sure to trigger many situations similar to this - so patience is the key here.
I like BOSS a great deal and I believe that Vik and the rest of the team behind it have a vision for opening up search to encourage innovation. I also believe that Microsoft has a much more open attitude nowadays (something that has taken a couple of years to turn around at an organisation scale, but they are now pointing the tanker in the right direction).
We only need to look at the fact that Microsoft decided to launch their, pre-bing-rebranding, Live Search API 2.0 at PubCon last year to see that they are keen to have an active base of developers (as Microsoft now see it as an advantage to have people cooking up all sorts of vertical/local/etc search engines).
I just can't see Microsoft dumping a thriving developer community (BOSS users) - I see it as being more likely that, given time, there is a move towards a system that mimics BOSS and possibly even moves away from the planned paid model for BOSS.
I would happily pay for BOSS usage, but I'd be able to put more resources into our search project if we didn't have that overhead on the horizon - a smart move by Microsoft (and of course Yahoo whilst the changover takes place, which may be over a year before BOSS is affected - if at all) would be to identify those developers who are using the Live Search and BOSS API's in interesting ways and give them all the support they need to build products which will serve specialist sectors.
As it stands, you can start developing and testing services with little cost, but you start to worry about the longevity of the system you are developing for (and the licence terms staying favourable) when you look into launching large services on them. We may have to wait, but I suspect that once BOSS gets towards to the top of the priority list we will see statements which are designed to comfort those driving innovation in search who are not employed by the big 3.
The other way to look at this is to go out actively support BOSS by building indespensible services on BOSS whilst there's time to influence the decisions that will be made in the months/years ahead. I'll be going down that route, even though it is a gamble, I hope there will be many others doing the same.
I sincerely hope that BOSS survives, and I'm not troubled by whose name is eventually going to be appended to it - as long as the values that gave rise to it are not lost along the way.
So I'm hoping for this to ring true:
Meet the new BOSS, same as the old BOSS