I just received my TA-15 a few days before the TA-30 became public knowledge. My initial reaction was to want the TA-30 for the loop, boost, reverb and additional power, and I considered returning the TA-15. But, thinking about it, I realized that the reason for the TA-15 purchase was to get a very compact, light, giggable amp, and it maximizes those attributes. Once you start going "just a little bigger", it's a slippery slope! If I want a louder, more fully featured amp, I may as well maximize those attributes and use my Mark IV, or buy a Mark V, which are much more capable than the the TA-30, albeit also heavier to lug around.
I've got a Dr. Scientist mini-reverberator coming to provide reverb for the TA-15, and already find Analogman Bi-chorus and ARDX-20 delay pedals work fine in front it. No loop, no problem, at least for me. I value the compact form factor and light weight of the TA-15 more than any potential incremental improvement in sound quality a loop might provide.