i guess it depends on what you've done prior to KO. i usually let it sit for a good while, 20-30 minutes often. most of the trub is on the plate, but definitely not all of it. some is definitely under the plate and settles down the hole into your plumbing underneath.
boss, i didnt just pull "1/2 -3/4" out of my cornhole. that's what i've seen repeatedly for my system and brews. hence the note that i brew 2.5 to 3gal batches, i.e. this is for MY system, ymmv.
which leads to a reason i havent done the "cut a hole and add a valve" solution- once you install it, it cant be moved. i do 5gal brews sometimes, and would probably suck in alot of trub. im leaning towards the pump solution, but been lazy and havent pulled trigger.
i dont think using a pump with a float would be an issue. if you used a filter, towards the very end it would just rest on the false plate, but it'd still be filtering. as long as it wasnt clogged up and the pump had enough suction there'd be no issue.
without the filter, you'd just need to keep your eyes on it as the wort level got down towards the trub. if you kept the float to the outside near the kettle wall i'd guess you'd be able to get a decent visual of its position/depth.
i should just bite the bullet and order a damn pump off amazon. talk is cheap, but actually trying it out would give us answers/results.