It´s nice to see some interest again on TTDPatch development. As you know, I´m trying to keep all my sets playable for TTDPatch, but there are some very few missing features which will make this impossible in the long run.
E.g., the upcoming release of MariCo needs two features which aren´t supported by TTDPatch:*
var2 "water class" (i.e., land info of nearby tiles (60, 62))
"bb" bits 5 .. 6 (from OpenTTD r22655) Water class: 0 - undefined / land; 1 - sea; 2 - canal; 3 - river.*
action1 would need <num-sets> as an extended byte. This is most important for newobjects, since they always only have one "view" (<num-ent>), so one cannot take advantage of this element being an extended byte (like one can for stations), hence an action1 block can only hold 255 real sprites.
OpenTTD >r22925 includes this feature as part of its "extended format" for action1. Supporting that "extended format" for TTDPatch as well would be a nice move, but only introducing that extended byte format would suffice, given it´d be the easier implementation, and would make MariCo v0.23 playable in TTDPatch again. (OTOH, this would again be an incompatibility issue ..)
I´m posting this here mainly as a note, to keep this in mind. This should not be regarded as a threat to implement it ASAP.