I struggle and I wonder... What would suddenly happen if there's no 'new' SBD's being printed? Steem mcap will rise to 'balance this situation' which will lead to more SBD being printed... which will lead eventually (again) to reach this 5% limit.

Indeed, there are two things to consider here:

(1) the Steem market cap will indeed "rise to balance the situation" until that will become impossible to achieve in the short term. As I've said, a Steem market cap of about 2 billion USD, so Steem at a price of about $8.-, is plausible to achieve in the short term. For the "5% protective blockchain mechanism" to take place, that would require 100 million circulating SBDs.(0.1B SBDs / 2.0B Steem market cap). Maybe via a few "pumps" temporarily an even higher Steem price is possible, but I don't see it sitting at that price point for months in a row.

(2) in order to grow to a circulating supply of 100 million SBDs will take quite some months; it's hard to closely predict exactly how many months because the inflation rate of SBDs circulating depends on the Steem price. But at the current rate we're talking about 1 to 3 years for that to happen. And that's quite some time from now, almost like "a century" in "crypto time".