Last year I made the switch from the KA2 to a custom built keyboard (Scylla kit from BastardKB) and I have been really happy with it. Keeps the curve of the hand, has better thumb clusters (IMO), is split, and has full customization through QMK. Plus it was fun to try building my own!
there were a couple projects at one point that did flexible replacement PCBs for the Advantage2 that would upgrade the board to QMK (Stapelberg?) – could use it as an excuse to update switches and keycaps?