Kost
I'm sure you already know the v3 28/2.8 has a 49mm filter size (kind of big) with slip-on type hood. There are 2 versions of the hood: one with a cut-out and one without. The v4 elmarit 28/2.8 that Tom A. mentioned has a 46mm filter size and also has a slip on hood (with cut out). I don't think the v4 hood will fit on a v3 lens.
I don't remember how bad the finder blockage is for the v3 as I only placed one on my M2 briefly (tried a friend's lens at a dinner party), but I remember it definitely blocked part of the M2 finder (of course has no 28mm framelines). I currently have the v4 Elmarit and it intrudes (the hood actually) on the 28mm framelines of the M9 (0.68X mag.) as well as the M2 (0.72X), but not badly. The cutout helps. I would imagine the v3 with its larger diameter, and longer lens length, and bigger hood (possibly without a cutout) intrudes substantially into the M4P view. Not sure about the M8, but likely.
Having said that. People seem to *really* like the results from the v3 Elmarit. Quite a bit.