before you reach that limit you'll upgrade to 50MB and quantitative ease another 10 million btc into existance to cover miners - that's how it'll end up. (not really because people won't even use the 20MB version)
What plausible reasons can you give for either of those assertions?
Why *wouldn't* people use the 20MB version?
Why *would* the network majority agree to create another 10 million BTC?
-you propose to raise the limit without an immediate need now - you'll do it again (what else)
- why they wouldn't use it has been explained already earlier
- the majority will have to agree on that later because mining becomes unprofitable once the inflation fades out - especially if not the number txs actually do occure what you project (in case your fortune telling skills fail, which they will)