I've been wanting to post this for a very long time...so glad to be able to share at last some real news. Advance warning - it's a mix of good and bad.
Updated firmware has been released for the P1 Gen 2, P53 and P73. IMPORTANT NOTE: It's available on the Lenovo support website (find the platform, go to downloads and drivers, grab it, unzip it and use fwupdmgr to install the correct .cab files - be careful to get the right one for your BIOS).
It's not on LVFS yet but we will be adding that - I don't have an ETA (I'm asking for it) but I hope it will be soon. I recommend waiting for LVFS to be available - it will make updating easier. For those who are twitchy and choose to go for it let us know how it goes and I'll make sure any feedback gets back to the thermal team.
I've been able to try the P1Gen2 version (I don't have a P53 or P73 available - one of my colleagues will try that but it's a holiday in the US). I'm still doing some early testing myself but I have been able to run a kernel build with no thermal throttling.
The other good new is we have two more platforms getting the update - T490s and X390. I can't share the date for those yet but they are in progress right now.
And so to the bad news...other older platforms are unable to get the update. The reason is related to the thermal firmware that is used on those platforms - it's an older version than the platforms we have updated and is not update-able to use the same mechanism. The thermal team have looked at it and determined it's not feasible.
As pointed out by @notabenem above I have been keeping an eye on Matthew Garrett's reverse engineering of DPTF and helping out where I can. I want to make sure that implementation doesn't impact Lenovo platforms which have the improved thermal firmware but I'm also hoping to find a solution to improve things for those who have platforms that can't be updated. I'll continue to help out there however I can.
All 2020 platforms have support for the newer firmware.
Let me know if any questions. I'm hesitant to post this as I've not been able to do proper testing yet and I'd rather share once it is on LVFS but waiting longer once I got permission to share something seemed wrong at this point.
Side note - when I did the firmware update I had to hit F12 at boot to get the boot menu and select 'Linux-firmware-updater' for the updater to run. Not sure if that's peculiar to my system as it shouldn't be needed. After that the firmware update takes a while so be patient.