In an honest-to-goodness innovation, Twitter has constructed a mechanism by which people can add items to their Amazon shopping carts by tweeting in response to things such as revenue-raising advertisements. There may be hope yet that even with Peak Twitter talk afoot, a serious revenue stream could launch the firms revenues to heights commensurate to the firms self-perceived importance.
I haven't been seeing a lot of "peak X" action over the past few years.
But maybe I just haven't been paying attention. There was "peak Facebook", "peak banana", "peak Rob Ford", and even "peak punctuation" — though "peak Chris Christie" didn't get the play you might think it deserved.
Among similar constructions, "maximum X" and "minimum X" are common — but there's no "valley X" or "trough X" corresponding to "peak X".
For some substantive background on the "peak twitter" talk, see "The last txt, the last tweet", 5/3/2014.