Zen who do offer both BB only and a BB + line rental package that is WLR...
Zen line rental is always WLR3 at the moment, but this could change.
Zen's Phil Long has indicated Zen may start providing ADSL2+ at exchanges where Zen has presence from the Zen MSAN. This will be SMPF unless Zen also start offering POTS from the Zen MSAN (a possibility, though not one I'm aware Zen has commented on).
Zen FTTx customers at Zen served exchanges were switched from BT Wholesale WBMC to Zen backhaul en masse. I have no problem with this - those customers are likely to receive a better quality service than over BT Wholesale WBMC, and there's no contractual commitment by Zen to continue delivering services in the same way.
It is certainly conceivable that one reason behind Zen's decision to market their new fibre broadband products primarily as fibre and phone bundles is because they intend to start providing POTS over MPF from their own MSANs in the future. If they have customers on packages suitable to be switched over to Zen MPF POTS, it provides the commercial justification to launch such a service.
Zen already provide VoIP services, so with MSANs in the exchanges backed by an MPLS network, they're not missing many of the elements needed to offer POTS and Fibre Voice Access (on FTTH) services.
As Zen seem determined to keep offering 'broadband only' products, you will always be able to avoid MPF by selecting a non-Zen WLR3 provider and taking Zen's broadband only service.