So we don't have to fork next time, and we don't go x20 in one tine
If we go x20 in one time it will not make the used space 20x bigger instantaneously. If we had a 20MB limit right now it wouldn't matter because blocks will be filled by the same amount.
The 1MB was antispam mesure, so growing the limit slowly can be good for same reason.
and mostly, as the limit would be calculated by the software, that would mean no need to fork again when 20x will not be suffiscient anymore.
I read somewhere the issue is most with bandwith, I didn't even think of it because where I live, I have fast unlimited cheap connexion
So raising the limit slowly will stop the blockchain spammers? That makes no sense. If they can spam at 2MB then they can spam at 1MB and at 20MB. We can find measures to live with the spam, but limiting the block size at 1MB isn't a valid solution for this.