just having a 68000 wouldnt necessarily make the machine as a whole equal to the mac/lisa/amiga/atariST/etc...
imagine if they did that - but had no custom chips - still used an MS-DOS type thing, and still had all the interupts and crap(quite possible), its still quite likely that the wouldnt have an automaticly configuring machine
the 640K limit would be gone! that would be good
it would of been interesting to see
but the amiga & mac(and many others) still had advantages over the ibm-pc other than the CPU
so perhaps in terms of sales and support and marketing and popularity - i dont really think it would of changed that much