osu!stream will have pc map support, yes.
osu! will have native support for os x via mono in the future. building from scratch is not the correct way, in my eyes. i mean sure, you will get something working and it may play maps, but adding all the features required for a full-blown osu! is just a waste of time, when that time could be spent on making osu! run correctly under mono.
by the way, i am not telling you to stop working on this. just saying you will not have my official support for this kind of approach.
also i play on wine daily and have none of the said issues (except no HiDpi support, which isn't a deal-breaker for me).