There actually are a surprising number of uses for it on platform levels. PK Thunder Cancel I find to be the most useful on Battlefield because it basically gives you a few moments of invincibility because the hitbox covers your whole body and has very high priority which drags opponents if they touch you and combos immediately into almost any aerial. In addition it moves a lot faster than Lucas could normally once it's begun so you can lead it into PK Fire if the opponent is on the ground level for a surprise attack.
The timing on it allows for a ridiculous amount of variance on what direction you send yourself. On Battlefield from the top platform you can send yourself into a floorblast onto the next level platform, floorblast bounce to edge cancel, ricochet across to the other platform, PK Thunder cancel, numerous shallow angles sending you to the ground level, and directly backwards. That's in order from latest timing to earliest I'm pretty sure.
Also, if you notice your opponent begining to predict your direction or they aren't in a good place to hit them you can simply delay your thunderslide by sending the thunder out slightly before hitting yourself. Although this makes it more around the normal speed of initiating PKT2, you have complete control over your direction and can avoid the move getting shielded and punished. This is also useful if you notice that you've mistimed it and aren't going to get the outcome you wanted.
Some stages will almost always lead to ricochet PKT2 when done off the platform such as Yoshi's Island (Brawl) and Halberd. PK Thunder cancels are very easy to do on Lylat Cruise as well if you thunderslide off of the middle platform with the latest timing (depending on how it's tilting at the moment.)
Thundersliding can be great if you know your timings perfectly. I do it enough that I almost always get exactly what I want. I think it has the potential to be a big part of Lucas's metagame in time.