No support. Maps and mega stones give you megas and legendaries
which are supposed to be hard to obtain and you are supposed to
work for them so just throwing them as a reward for rumbling would
be too OP.
No support, you get boxes & keys from rumbling as is, those have a
chance at giving you summoning items and rarer gems (dragon, fairy,
etc), rumbling is fine the way it is.
Mega stones are already easy enough to get now with the new fishing
system implemented, so it really isn't needed.