As I am a heavy wetter, a more absorbent diaper is attractive. One limitation of superabsorbent diapers that has been mentioned is the failure of the tapes to support the weight of the diaper when near its maximum absorbency. That is one of the reasons why I wear a onesie now with my premium diapers. With a superabsorbent diaper a onesie would be even more highly recommended. Of course, one also could reinforce the tapes with a small strip of duct (or Duck) tape.
WetDad mentions the all-SAP diapers swelling up so much as to be noticeable. I think he is correct and that may be almost unavoidable. However, a diaper with fluff pulp would bulge equally as much at capacity and also would be thicker when dry. As Tarlton mentions, loose pants help to conceal bulges. Of course, one of my favorite IC sayings is "It is better to Bulge than to Leak."
Patrick mentions the benefit of high capacity when traveling. For long interstate trips I diaper as I would at night and even add an extra layer over the diaper in case of leaks. When I go into a restaurant to eat my diaper bulge could be noticeable. With a superabsorbent diaper that probably would not be necessary.
The new Rearz Mega-Inspire that Tarlton mentions advertises a capacity of 8,500 ml. and is available with a plain white shell. That would seem to meet our requirements for a "mainstream" high-capacity diaper as it also claims having tall standing leak guards. This could become the rival to MegaMax if it finds a "mainstream" vendor. Thanks for the tip-off, Tarlton.
And as HDT mentions, the real issue is not absorbency per se but "leakage." If it leaks, it does not work, regardless of the claimed absorbency.