I think under the "we're all consenting adults" doctrine that it should be allowed. If you really want that behavior, why force the char*/%s dance at each call site when it's easy enough to do it in one place? I don't think anyone supplying a width would really be surprised that it would truncate the result and possibly break round-tripping through repr.

Besides, it's allowed in pure python code:
>>> '%.5r' % object()
'<obje'