POE gets enough player growth from the new expansion
You see people posting weapons that dropped with 4 perfect T1 mods and two open slots every now and then. It's not a huge stretch to get 4 T1 through drops or chaos spamming. From there, it's only like, one in 50k or 1 in a milion to go from 4 T1 to 6 T1 depending on the mods you need ;). Like, if someone manages to find a weapon with T1 flat, T1 %, T1 hybrid, T2 attack speed... granted, that's absurdly unlikely, but it is within the realm of possibility.
Probably happens more than you might think, given the quantity of items rolled every league and the fact that people will chaos spam more. Yolo exalting the perfect two suffixes is not that unlikely, given crit chance and crit multi are both relatively common rolls. The main issue for standard, though, is the amount of eternals people are going to hoard as a result. There will likely be a loath bane replacement, and it's going to be the product of eternals.
of course there will be a loath bane replacement. in standard only, though. without the use of eternals in temp leagues, it's impossible. even if all the new temp leagues merged into a new standard, it would be HIGHLY unlikely. however, that's what i'm hoping for. a new permanent league that isnt effected by the irreparable damage eternals caused. I do not want people to think that the general dagger build goes like mark of the doubting knight>binos>master dagger>loath bane. Lethal Brigade is not a unique item (mechanically speaking) but it is referred to as such because it is the only item that is the absolute best. thereby giving the crafter the monopoly to what every single dagger build will eventually want. while i have nothing against that, i do have things to say about mixing the solution to the game with the very problem they are trying to fix after three months have passed.
Maybe if Path of Exile gets enough player growth from the new expansion, they could consider opening a new permanent league, but I highly doubt that's going to happen. Their reasoning has been that it would split up the playerbase too much. Plus, I imagine there would be just as many people pissed off by a new permanent league as there would be people who are happy about it. It's just a lot more elegant to have a Hardcore permanent league and temp league, and then a Softcore permanent league and temp league than two permanent leagues and one temp league for each ruleset.
The other problem is opening up a new permanent league is almost certainly a death sentence for the old one. In effect, it would be more of a replacement, which kind of ruins the appeal of a permanent league for many players. I wouldn't personally care as I only really care about the temp leagues, but I imagine there would be quite an uproar.