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.

regards
Michael