It looks like the way the next update (2.3) is going to change exploration payouts and ranking is final, so here's how that'll change Elite Plus requirements. I thought I should tell everyone this, so that people who might be close to it would have advance warning.
The current requirement for Elite Plus status is basically that you earned your Elite exploration ranking via scans only. (No passenger missions.) Right now, it's at 155 million credit profits from exploration scans.
After 2.3, it'll be 600 million credits, in order to keep up with the changes and have the new requirement be on equal footing with the old one.
Here's how I came up with that number:
First, an interesting change will be that only half of exploration scan credit payouts will count towards rank progression. Right now, it's a 1:1 ratio: you sell data worth one million Cr, you get rank progression worth one million Cr. I'll just call these exp, as in "exploration points". After 2.3, it's halved: you sell one million Cr, you get half a million exp. So this change alone would halve the Elite Plus requirement - but this change isn't the only one.
Second, and more importantly, the exploration payouts for most bodies are increased, up to 5-9.5x for the valuable planets. You can see more data on this
here. I decided to go with an estimate of 8x average increase: if you scanned the same amount of valuables, in 2.2 you'd get 150 million Cr for them, but in 2.3 you'd get 8 * 150 M = 1,200 million Cr. That would be your bank balance payout, mind, not your exploration rank progression. Halving that as per the above, that would be 600 million exp: enough to become Elite almost four times over.
The new number for Elite Plus (going with a 8x increase estimate) would be 620 million Cr, but I decided to "round" that down to 600 million, as that's easier to remember.
So, there we go.
This will apply to any screenshots made / submitted after 2.3 goes live, so if you're near to getting Elite Plus status and are shooting for that, I'd recommend doing so before the update hits. I'll update the post and the OP once we do have a launch date.