The nuances of this plan are hard to suss out, partially because it scans as transparently terrible, but also because Tyrion hasn't had much screen time to get into the nitty-gritty details. The show's creators David Benioff and D.B. Weiss seem to be saying, "Trust us. We got this."
But do they, really? The benching of Tyrion -- along with his fellow string-puller Varys -- suggests that Game of Thrones has undergone a gradual change over the last two seasons from a tough-minded, bleak show primarily about machinations of power to a more fleet-footed, zippy adventure series about conquest. Conventional heroes, like Jon Snow and Daenerys Targaryen, are more important to the larger narrative of the show now. There's less room for a figure like Tyrion -- unless he's about to undergo his own dramatic transformation.