at the moment seg wit is on the table, and those who are working towards [other solutions] don't have feasible code that has gone through the vetting process.
Well, no. BU has been running on the main chain several times longer than has The SegWit Omnibus Changeset.
I repeat ... the BU code that's actually running on main net at the moment (and therefore being 'tested' on main net) is mostly the old 0.12 core code.
None of the new block size related code is being exercised.
Bugs in the old core stuff are most unlikely since it already ran for so long (and had it's bugs fixed way back when).