I find the above confusing: best gues is that the proposal is:
'normal' terracotta would be changed to behave as glazed terracotta now does (can be pushed but not pulled by sticky pistons and does not attach to slime blocks)
glazed terracotta would be changed to allow a sticky piston to BOTH pull & push these blocks (but its non-attachment to slimeblocks would be retained).
Assuming the above is an accurate interpretation:
Having a block that was movable by sticky pistons, but not by attachment to slimeblocks would be an interesting change that would offer new opportunities for builds.
SUPPORT the introduction of such a block.
I would prefer, however, to assign the new behavior (interacts with sticky pistons but not slime blocks) to a new block so as to avoid breaking extant builds. [An alternative would be a 'super-sticky' piston that could move glazed terracotta (and potentially other blocks such as hoppers), but that might be seen as tooo far outside the scope of the OP.]
Rollback Post to RevisionRollBack
WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.