Using large DFT for OFDM to avoid the guard interval
Sure,  you can !
Practically, some systems are using OFDM system with number of subcarriers 4096, but the PAPR will be an issue in that case, and if your channel is fast-fading, the time-domain equalizer will be high-complex since one-tap frequency-domain equalizer will be useless.
Usually, choosing the length of the symbols depends on the channel delay, e.g., if your channel delay is 128,  you must use at least length of symbol 1024 and so on.