Why? Do you a explicit, specific need for the 80 bit Extended? Note that Intel has always said that Extended was intended for intermediate, internal calculations and that it shouldn't be generally used unles strictely needed, so it "dissapearance" shouldn't come as a surprise.
When doing high precision searches, like finding small differences between sums of square-roots, extra bits help for pre-selections
(see e.g.
https://topp.openproblem.net/master.pdf problem 33 or search for "Erik D Demaine open problems problem 33')
Puzzle: Which one is bigger:a) sqrt(13274) +sqrt(26086) +sqrt(37407) + sqrt(95*95)
b) sqrt(24417) +sqrt(35473) +sqrt(48634)
(hint: extended type will not help here)
However, I am rewriting my arbitrary fixed point unit to work with doubles and it seems to run faster, especially on an AMD Ryzen processor, not that much difference on an Intel Core-I7.