Mythic may indeed give the trinket an opportunity to shine, but so far it's been quite lackluster for AS in normal/heroic. The proc is incredibly sporadic and as AS, sometimes the "swp dump" into proc doesn't seem to be much of a dps gain, requiring 4+ consistent targets hit. The trinket seems very gimmicky/padlord-y for AS and sadly M Assault/M Iskar might be the only fights it's good on. H Archi, H Xhul, H Mann (and their mythic counterparts) could benefit from PoF as well, but these are even more RNG/unreliable than Assault.
If there's a spriest whose found great parses with it on heroic/mythic, I'd be very interested to hear your thoughts and view logs. Atm I can't see it consistently outperforming Iskar trink + Piston trink combo.