Well, let's see...
...can't sell ISK for RL cash without a ban, so obviously no use for ISK outside of the game...
...not much to do with all the ISK I have since I'm barely actively playing, so most of it can be allocated for PLEX purchase without much flinching even assuming all debtors end up defaulting and I'm left just with my current assets and none of the loans back...
...about 10 more years minimum of vague interest in EVE, probably a bit optimistic, and can always switch to cash payments anyway if interest re-surges after most ISK is gone...
...so, I guess somewhere about around 2 bil ISK per PLEX would still be quite damn comfortable for me personally, and probably would have to go above 5 bil ISK per PLEX before I would go "eh, screw it" and only reactivate once per month or so instead of keeping it perma-active.

...

HOWEVER

...

On the reverse side, say I would be nearly ISK-less but my interest in EVE would have re-surged, so I'd have to start from the ground up.
In that case, I'd probably purchase a small lump of PLEX with cash and sell for ISK even if PLEX would only sell for about 100 mil ISK a piece.

Really? God damn that's sad.

Before you find the cost unbearable and start paying montly subs or just quit EVE?

After 6-7+ years of playing Eve and after pretty much doing everything, I can't seem to get into it anymore. At times I want to but that quickly fades.

Also being US and usually my play time is 6am-11am EST doesn't help either.

i already pay $, i its gotta suck to throw 500mil away every 30 days.

If youre grinding ISK to pay for your game instead of finding a real decent work, youre doing it wrong IRL.

I always thought PLEX is there mainly for people trying to buy victory and have more pew in bigger hulls, I only met a few children nerds who are too useless to make money to pay with.

I always paid cash for my subs. Had four when I was playing. Tomorrow I will have none. Always wondered why it's supposed to be so cool to plex your subscriptions with isk. Somebody has to put some cash into the game or there won't be a game. Not that I'm all that bothered by the thought, but I might want to come back one day.

This game is cluttered with people who want to convince themselves that they're better than other players for reasons x or y. Just like most other games and real life. I've gone back to playing solo pc games and have much more peace of mind now. Plus lots more time to live real life. MMOs are not for me.

When people make over $175/hour, grinding in-game for ISK is silly when you can just work for an hour and buy billions. I'd rather work for an hour and spend $30 for my five minutes of work or whatever for my two accounts. Which I've canceled anyway.