Looks like Hasbro are prohibiting unlicensed artwork as well,
according to this. Admittedly, the artist tables have only been numerous in the last 2-3 years, and since IDW don't sell posters, I don't think anyone (including IDW) were objecting to fans & past/present Comic Artists selling posters & prints of TFs characters.
I know that a lot of fans like buying/requesting certain characters being done, especially by past/present comic artists... so I think this may hurt more than it helps. Especially to FunPub, who are losing a lot of revenue from the people (artists & dealers) cancelling tables, as well as the people not attending now if they can't buy custom figures or artwork.
I think the Dealer Room is going to be pretty empty this year...
FunPub have always neglected the non-toy elements of the Transformers convention (the guests, events, the annual meeting up with friends socially), so now that Hasbro are putting the squeeze on the one element FunPub always focussed on (to get in the toy dealers and scalpers), they've left themselves with an event that doesn't have much to boast about.