If this happens, will MFS attempt to police the meet point and force anyone who is currently providing "transit" to purchase and user this "product"?

I don't see how they'd differentiate the traffic..

Will it change/worsen the performance of the heavier traffic sites by "stealing" customers from the larger traffic sources, and then dumping traffic upon those already overloaded circuits making the HoLB problem all the worse?

If this happens I'd suggest everyone at the NAPs deploy some type of MAC-layer filtering. It's far to easy (and seemingly common) for providers to forget to set "next-hop-self" on NAP routes .. so what I foresee is providers selling transit via the exchanges ...and then never seeing the traffic bound to *their* unsuspecting peers.

Does anyone really care whether or not transit is sold over the MFS meet points, and if so, what are the operation concerns?

I personally don't think it's a good idea, there are enough traffic related problems without "additional" transit-only connections. Perhaps this is MFS's ploy to sell MAC-layer filtering ;-) -danny