That would be a little pointless really. Xthin turned out to be written incompetently, and we have a thin blocks relay protocol working now without Xthin. What next, fix Xthin so that it works with Compact Blocks?

Xthin devs (the Classic team, isn't it?) should quit while they're behind, IMO. They had their chance, they even got to market first, but it wasn't good enough.