I didn't win the lotto but sure there's always Saturday draw I will be buying that bike with rohloff hub obviously new  wheels Schmeiches Hub and light up front gates belt drive 35 mm tyres  tubes ,so did j must anything,the drugs are kicking in falling asleep here.happy thoughts my cycling friends.

Will a belt drive option be available?

On small / medium sized frames 26 inch wheels do give worthwhile clearance benefits - but it sounds like 700C / 650b on all frame sizes.

I think there's very few scenarios where the difference between 650 and 26" is significant enough to warrant offering both.  There's only 12mm difference in the rim radius and you could half that by going down a tyre size.

Quite narrow tyre sizes as well - possibly due to the carbon fork - so difficult to see it as a gravel bike with 700C 32mm / 650b 38mm tyres.

They do seem to be promoting it as the one bike for everything, I've already expressed my scepticism.  The tyre restriction is the fork, I'm a bit surprised they've stuck with a QR aluminium steerer one, there's plenty of full carbon thru axle alternatives, some of which have better clearance. I'm not sure I'd want bigger tyres on a Mercury, though if it's going off road the mud clearance might be useful. The frame itself is advertised with :

Tyre clearance:
700c: up to 40mm (35mm with mudguards)
650B: up to 50mm (with or without mudguards)

There's a picture of a complete 650B bike on the SJS website. Already sold, some lucky owner
https://www.sjscycles.co.uk/bikes/new-thorn-mercury-40-650b-with-rohloff-straight-bars-61l-gunmetal-new/

Is that a mid-drive motor and an IGH?

Spotted in Chester UK. Much loved!
 Note the derailleur as the owner had fitted a motor so no EBB. S&S couplings.
Great guy to talk with.