i develop on mac laptop running osx, but the tests are on unix boxes, ubuntu and i think debian, doesnt matter as i am not using any external libs other than pthread for the core. i only use curl for getting external website prices and that requires openssl. recently our config devs got iguana working on windows too, so it should work there too, but i dont think anybody has tried a btc sync on windows yet
i dont think segregated witness will activate anytime soon and in any case it is backwards compatible. I dont know why they dont just increase the blocksize to increase the blocksize... Implemeting a parallel blockchain to increase blocksize seems very contrived and a lot of work, so not sure when I will directly support it.