IMHO, the easiest way to do that is to propose lenses unheard of in the DSLR world.
Cheers,
Bernard
How will this actually help them?
Canon/Nikon/Sony/Zeiss/Sigma can design all the niche lenses they want, but the fact of the matter is that the vast majority of photos by most photographers is taken using the same few lenses. The exact lenses may vary, but very few people maintain a large collection of lenses and actually use all of them on a regular basis.
For instance, a wedding photographer may live on the 24-70 and 70-200 f/2.8, as well as a fast prime of some sort (85/1.4, 105/1.4, possibly 200/2) while a (non-studio) portrait photographer might primarily use the 35/85/135mm prime combination. A wildlife photographer might use a 500/4 and 200-400/4, while someone photographing property might primarily use a 12-24 zoom and 17/19/24mm tilt-shift. Someone who shoots a bit of everything might have a wider collection of lenses, but, for any one purpose, is likely to be using the same few lenses.
The point is, once a manufacturer has the bases covered, introducing more, niche lenses is not going to win them much more market share, or attract new users outside of that niche. You can do all sorts of things with optics, but there's a reason certain types of lenses are popular, while others are rarely-used - Nikon is hardly going to win many more users if they introduce a super-fisheye with a 220-degree FOV, or a 1-10x 'super macro'-type lens. Nor is introducing more lenses that pretty much do the same job - once you have a 'no holds barred' option and a 'budget' option, you don't really need much more in that category. Rather, it is the quality of lenses covering key capabilities that wins users, and that's something that all the major manufacturers can do relatively well.
With regards to the smaller flange distance allowing for a greater range of wide-angle designs, that's only true to a limited extent, and largely only for lower-end lenses more concerned with small size than optical performance. Digital sensors and their microlenses function best with angles of incident light that don't deviate too far from the perpendicular. Even if they didn't, a greater angle of incidence (away from the perpendicular) results in greater vignetting and greater chromatic aberration. So, the smaller flange distance may allow for some smaller, low-end wide-angle lenses, but the high-end ones will still need to have a retrofocus design. Sure, you can put the rear element closer to the sensor than you can on an SLR (this goes for all lenses, not just telephotos) but this represents a mere reshaping of a few elements to move the focal plane closer to the rear element, not a radical change in design (such as a Z-shift or curved sensor might allow), and isn't a significant saving in size or weight. Significantly reducing the size of lenses is going to require a revolution in optics, not a minor change in flange distance or mere evolutionary change in optical design or manufacturing precision - something which Canon, if anyone, has the lead in, with their advancements in diffractive optics.
As for the future of APS-C, that's an interesting and completely different tangent worthy of its own thread...