IIRC Xiaomi did this with RedMi 1S. after release when people complained about heat, they just released a patch which lowered the clock speed which inturn affected the performance.
Can you provide a source where they said this, interested in seeing the article
is there anyone else who successfully implimented 810 without reducing the clock speed?
*forums.oneplus.net/threads/oneplus-2-rumors-we-are-mad.316975/
No optimization apart from a smaller process node can fix the mess which the 810 is. Now Qualcomm has a boatload of 810s which no one wants. So they unloaded their junk to OnePlus, who, being fantastic software programmers, decided to heavily optimize the android operating system and somehow with great difficulty managed to underclock the chipset.
And for your second question the answer is
No, no one has managed to tame the 810, I doubt a chinese company with near non existent R&D budget will be able to do it.