Will 28/1.7 do ? If so you have the perfect excuse to get a Leica Q3
Not really, not on that tier. It's not that much of a difference going from f/2 on the 28-70 to f/1.7 on the Leica.
I'd rather buy a budget 28mm f/2 to f/1.8 for personal use,
or a 28mm f/1.4 L for work, than spending more than I did on my main camera and main lens together (R6 + 28-70mm f/2) for a secondary device.
Whatever 28mm I buy, it can't be more expensive than my main gear. Don't get me wrong, I very much like the Leica, I've tried the camera and I'd love to own it, but it's not the tool I need.
For now, I have the RF 28 pancake for personal stuff, the 28-70mm f/2 for work, and I recently added the RF 45mm f/1.2.
I need at least one fast prime between 28 and 50mm, preferably on the wide end, with an aperture wide enough to be worth putting down the 28-70mm f/2, when the light is not enough and flash is not a possibility.