We'll see it start to do much now that the limit is actually being reached. In the process of syncing the block chain, the first three fourths of the blocks take up one third of the hard drive space; that means one fourth of all the blocks take up two thirds of the disk space. Thanks to the limit, these ratios will begin to even out.
You forget to say once the limit is reached, Bitcoin popularity (crypto market share) will start to decline pretty fast. Basically only limited transactions can be included in the block, if more transactions are required by users, some have never to be included. Basically it will be easier to use different coin than feeling the hours/days/never confirmed transactions pain with 1MB Bitcoin
Popularity among who? Maybe the redditarded change tipping hammer lickers won't be interested anymore, but I don't see the future market makers of the world shying away just because they have to start paying a fee to use censor-proof inflation-proof perfectly fungible money.
If it's "easier to use different coin" then go do that; we won't miss you. Actually that's what USGavin is proposing anyway; the fork creates an altcoin.
No, im pretty sure the 20 MB (or whatever) limit will be active when at least 95% of miners agree. And such hard fork happened already and we still call it Bitcoin not alt coin.
If your really serious about Bitcoin being most popular crypto in future as well, please update to average computer/internet and you will be able to use full node after the planned Bitcoin limit improvement as usual.