I wouldn't worry about that too much. We are focusing on our struggles against low blocks because we have faced them so poorly this year. Overall though, we haven't faced them too much and won't next year by the time the new man gets here.
We are very unlikely to be back in the conference league next year through finishing high enough in the league. If we are in Europe it'll be in the higher-ranked Europa league where we will meet less bus-parking, once-in-a-lifetime-chance-to-kill-a-game-at-the-famous-Selhurst-Park merchants. It will remain the case that far fewer premier league sides will park busses against us than will take us on.
Overall, I don't feel like beating low blocks is high up on the list of qualities the new manager needs to have.
I also don't espsically hold the absence of that quality against Glasner. There is as much to be said for a settled approach as for tactical flexibility, and if he feels a 343 with 5 defenders and 2 holding midfielders is the likliest route to relative success for Palace overall then thats his call. Its not obvious that he's wrong, and nobody was moaning about it last year. Perhaps he has been taken by surprise by these frustrating games against unknown European minnows, or perhaps he expected it but felt it was not so big a problem as to justify moving away from the system the players are familiar with. We are, after all, still in the competition.
Either way, this is probably the only season where we will even remotely care about how to beat low blocks. I expect we will soon revert to taking advantage of that approach far more than being frustrated by it!