Pluto is too small and distant to show as anything but a stellar point in even the largest apertures, except that Charon might be resolvable separately from the planet, if the seeing is nearly perfect with a very large aperture. Allan has been trying for Charon with the 32" but has not had the seeing for it so far.
Pluto reaches about 0.1 arc seconds diameter near opposition. That will be near the limit of resolution with a 48" aperture or so, but Pluto's surface brightness is low since it is past Neptune which is about 4 magnitude lower surface brightness than Jupiter. That means that the magnified image for resolution would reduce surface brightness well into the mesopic range, making resolution of a disk about the size of the spurious disk quite difficult visually, even in perfect seeing.
As for aperture required to see Pluto, it still just comes down to how deep a person can go at a given elevation in the sky with their scope and conditions. Pluto is perhaps 14.4 magnitude and I can reach ~15.0 with a 4.33" scope in relatively steady Bortle 2/3 skies. But that is for objects higher in the sky. I lose a few tenths with Pluto lower in the sky. This has been critical when I have tried with a 3.15" scope in Bortle 1 conditions, since the sky wasn't steady enough down low. I have reached 14.3 with that ED80 scope higher in the sky in Bortle 2/3 conditions, but was getting stuck at 14.0 around Pluto's position lower in the sky.
I have no doubt I could see Pluto with a 4" ED refractor from my normal observing sites in good conditions, and I suspect I could scrape by with a 90 ED, but every tenth magnitude makes it tougher. I would probably need to catch it closest to opposition to take advantage of any Seeliger effect. There is also some known variation in brightness depending on which face is toward us (albedo variation) so there is some luck involved...unless someone takes a look at the albedo variation and ties it to the orbital position to find the maxima in the 153 hour period.