I don't think so. Games like Age of Empires allowed you to use every tile in the game and I don't recall reading anyone saying it was bad in performance. I think DSG did explain some of the reasons behind it at some point. Still, I'm pretty sure the game can use more without going haywire.
I remember I found some bug in the Editor during the Beta that appeared it would allow more than 8 tiles, but I no longer have that particular map.
P.S. — But yeah, it was pretty mean of Blizzard to do that when they know people have been trying to break those limits for some time, both in RP and AWS-like maps. Fortunately, I believe that Decals can be used as a workaround.
Weren't we all? :/
Despite being the only one who posts here (so it's easy to think so), I'm not actually at the head of this mod. Now, from chatting to the members of the team I've tried to catch we seem to be awaiting the release of another mod containing certain assets we've been given permission to use before we continue implementing the human race.
That's all I know, as soon as I know more I swear - I'll share!