If at all possible, I'd like to request support for, as the tittle says, OptiFine's connected textures feature.

New Glass with Connected Textures, for example, does this for vanilla glass panes and this is what's shipped with OptiFine by default.

Adding this mod's blocks to matchBlocks in resource pack's .properties file sort of works, but there's a bit of an issue with top\bottom faces. I.e. they do not disappear, but side faces (north, east, west and south) change correctly.

Nvm, I've read the mod's comment thread about this.