Even if MS doesn't support GAPI on a future platform, it would be trivial to create a gx.dll wrapper that utilizes DirectX for direct display access.
At this point you can't go wrong using GAPI (or PocketHAL - they both just give you a buffer to draw to). Just try to make your game flexible enough to support other resolutions without requiring massive amounts of changes, as the new VGA devices are already on the market.
Dan East