This was asked recently, and although the VM reply in the forum is non-committal, you can work out that the LU hotspots are being discontinued relatively soon because they will be replaced by this. VM have written it into the T&Cs to avoid customers have a valid complaint when there's a gap between the hotspots being discontinued and the new service becoming active. And as most people sticking with VM will re-contract every 18 months, the number who might demand access to LU hotspots will be declining fast. In the second link you'll see canned press statements attributed to VM and O2, so there's some form of announcement, but they're being a tad cagey.
Note the reference to "all major networks". There's obviously a cost to this system, and it's not clear that all MVNO will choose to join.
