well sakurai prolly knows what hes doing, he realizes (i hope) that meta/pit can come back easily to the stage. so he'll put (i hope) a counter to glide, so the game's not broken.
well there are counters like d-air or FSJ, but when, as some said, top players DI upwards then come back at the top of the stage or do something even more disgusting.......wait, we already got a counter to that; *puts on a cap* IVYSAUR, BULLET SEED!!! then combo till death...
for other characters, they might have like strong u-airs or fast/long ranged up smash, and dont forget projectiles that can interrupt their nice and pleasant flight...thank you for choosing, death-to-glide-abusers airline, we all hope you wont come back on the stage.
what i mean is, gliding is predictable, cuz it seems to be pretty slow. and, if he comes back from/on the top of the screen/stage, well, just wait for him to fall, cuz he'll have to stop one day, since he can't change direction. yea, just wait below the glider preparing your grap or up-smash or whatever, if they start gliding then you shouldnt really care about edgeguarding; glide speed<<<<<<<wavedash/SHFFL/jumpspeed