Tier or award points?
I am no expert, but I believe premium economy only earns 100% TP on BAEC. As for avios, also only 100% for some of PE fares.

For tier and award points, I expect something like this for AY new fare structure:
Econ lowest: 25% (perhaps branded light)
Econ, "flexible" (ie current KMPT): 50% (perhaps branded BA)
Econ, full flex (ie current YBH): 100% (perhaps branded VA)
PRO fare is vanquished

Premium econ, lowest: 100%
Premium econ "flexible": 150%

Eh, don't give them bad ideas.

And I cannot see semi-flexible and flexible getting folded as one single Value/Pro replacement. That would effectively be the end of Value, or it would be way-too-cheap for fully flexible.

On long-haul, good-ol' M (from before the type system) seems to be roughly 200€/way over the lowest discounted fare. And even that's nowhere near as expensive as H/B/Pro.

Just my two cents, but I do think it will be the end of the fare types.

I can't possibly see how they could keep 150% on PRO fares, that cost as much as a business ticket and at the same time offer 150% on a premium econ ticket that will sometimes sell for half that price.

This makes me think there is no room for all the types once PE enters. Leaving room for maybe 3 types in econ, 2 types in PE, and 2 types in J.
It think there will be a name alignment, adopting "Flexible" as the moniker for rather inflexible tickets and "Full flex" for tickets that actually has flexibility.

I believe this could lead to a gradual move away from traditional mapping of a fare to a letter code. You could then in theory sell every seat on a flight for a different price. I believe BA is experimenting this on some routes by having only one fare class code (F) for first class but they will of course still sell seats at many prices as explained in this post on the BA forum Link to post .

If that horror scenario realizes, I cannot see them reusing the existing branding. It just wouldn't make sense to call the expensive Value brackets as Basic and the current Pro brackets as Value.

And realistically, nobody buys M and K if they have the choice. It's just too expensive for just a little bit of flexibility. If there was demand, I would think that there would be a more straightforward away to book them than call CS.

I think it's more likely that they either keep the current system with 3 types in economy, and add 2 types in premium. Or that they go back to the old system with just to 2+2(+2), meaning discount and flexible in all cabins, with optional bundles on top.

Besides, I don't really the problem with keeping Pro at 150%, regardless whether discounted PE earns 100% or 150%. Only the most careless and unpoliced of flyer would squander somebody else's money on Pro just for the mileage. That guy can continue to buy Pro at 150% or switch to Premium, depending what his policy allows.

I can totally see Premium Flexible earning the same 150% as Pro, while Premium Saver would either continue to earn 100% (as it does in codeshares) or be upgraded to 150%.

Oh no, my flights usually book into R because I mainly do intra-European leisure flights (long distance relationship). Going for the cheapest (lol). As they get rid of R, what potential impact would that have? Will my ticket prices rise? Or will lower price fare buckets sell out quicker? Or will fare prices fluctuate with much higher amounts of euros than we are used to? Sorry I am a total noob with those fare codes as I qualify entirely by segments fo FF status.

As said above, the supply/demand situation and the competition in the market does not really change with the introduction of premium economy. Thus, Y fares (at least intra-Europe) should not be affected even if they adjust the fare codes and/or reassign some of the letters from economy to premium economy.

What a silly system where the number of latin characters dictate how many different fare types you can have.

Some additional Info from Finnair on the changes:

"Our new Premium Economy travel class will be in operation during spring 2021. As the sales for the new travel compartment start approximately one year in advance, we need to re-accommodate some of our existing booking classes to be used with the new travel compartment and its fares.

By removing booking classes P, T, R and W now, we ensure that there are no overlapping bookings in wrong travel classes once the booking classes are reintroduced back to sales during spring 2020. This change also enables us to align our booking class structure with our partner airlines, who also have a Premium Economy travel compartment.

(...)

After this technical change, we will continue to offer similar price points as with the removed booking classes by continuously reviewing the fare levels of other booking classes.

Somehow I think I've asked this before, but I don't remember anymore... What does L stand for if fare basis is QLVA2SE? I take it this is Q inventory, VAlue, 2-way ex-SwEden. But what about L? Sounds awfully light, but I want 100% points!

AFAIK it stands for "low season". But if I'm wrong, someone smarter will correct me!

Sounds credible. ^

Yes, it is "Seasonality code".

booking class "Q" + seasonality code "L"= low + fare family "VA" + RT fare indicator
"2" + country code "SE"