As my dr doesn’t really get used off road (nowhere to ride) I was thinking about having the front hub replaced onto an 18″ rim and then fit road tyres front and rear, would this work?

Useful info here:
https://www.thumpertalk.com/forums/topic/695757-converting-drz400s-to-supermoto-help/

I’ve just converted my drz400s to supermoto the cheap way by using wheels from a aprilia rs125 front wheel fits straight in but you need a disc adapter for the larger disc (£38 eBay) and a couple of washers for spacers rear wheel needs about 6mm taking of where the disc bolts on its a tight squeeze but it will go in.

17″ road wheels not 18″ or it’ll get weird handling.
Plenty from the same or different manufacturers will fit easily or Ecels/Talons
I have excel/Talon on the CRF450R in 17″” with 250/400 cc sticky tyres due to it only weighing 97kgs fully fuelled.
You’ll need to run then at very low pressures too – usually around 23-25 psi

10 years out of date there.

Out of date.? What a DRZ ? Yes your probably right but it’s still more reliable then my KTM