Well, if Nova really decided to block these SLM forever, that would be at least massively unprofessional, so I don't think they'd do that if they want to build confidence as a new player on the exchange market.
I mean to have read that for coins they delist they always gave a withdraw option. If the problem is related to change addresses, there is absolutely no excuse to not letting users withdraw their funds.
A little addition to the post about a "equilibrium PoB burn rate":
There is another option to change the equilibrium apart from PoB block frequency and PoB block reward: the "decay rate" of the "EffectiveBurntCoins" variable (explained at the end of
the "ELI5" on the website). I can imagine a slightly faster decay rate could make sense at a first glance; that would mean that people would only burn coins if they see a ROI in the next ~3 months for example (and not in ~1+years like now). It would, however, also mean that the effect to reward long term engagement (first paragraph of
the "Advantages" page on the Slimcoin website) would be smaller.
A faster decay rate would also decrease the average burn rate and make attacks on PoB easier*. The slow decay rate has an interesting side-effect: as "old burners" will try to find blocks at least until they make profit, the validator (=people that find blocks) set is pretty stable, and phases when few coins are burnt do not mean less security of PoB blocks.
Overall, I think the current PoB implementation is well thought out: it allows a high burn rate but doesn't make Slimcoin too deflationary to be useful as a currency.
*As the current protocol doesn't allow two PoB blocks in a row, a PoB-only attack can only try a double-spend to "scam" a person which accepts 1-confirmation transactions. As this is unlikely, PoB-only attacks are extremely unlikely, too - but they could be combined with a PoS nothing-at-stake or PoW 51% attack, so the security of PoB blocks has a lot of significance.
