Cross compiling is indeed a bit of an involved project, but generally is for any embedded system until you get the hang of it. You might also look at the similarly MT7688-based Seeed Respeaker thing - although they are using a different starting point and a different C library, it's likely a full-scale replacement of the Onion system with theirs could be made to work on the Omega2. Unclear if their hardware will ever ship, but starting to look like they have some repositories up. You'd need a version for the base board, rather than that using their add-on directional microphone array.