The phrase "arguably not yet" is correct and usable in written English.
It can be used to express a point of view that something is not yet established or confirmed, but there is a reasonable argument for that position.
Example: "The technology is arguably not yet ready for widespread adoption, as there are still significant challenges to overcome."
Alternatives: "possibly still not" or "debatably not yet".
The basic question here was what to do about an error arguably not yet plain at the time of trial but perfectly plain, given the intervening decision in Tapia, by the time of the appeal.
One that seems to have endeared him to the incoming general director at the Paris Opera, Stephane Lissner, is to develop ways of bringing opera and ballet companies into closer collaboration (a project also launched by the Royal Ballet in Wayne McGregor's stagings of Purcell operas, although arguably not yet carried through).
However, VR training environments have arguably not yet fully reached the potential of reducing training time, providing a greater transfer of expert knowledge; or supporting decision making.
New hires arguably have not yet settled in enough to crank out their full earnings potential.
Even Trump himself, arguably, has not yet traversed the chasm of scrutiny.
Arguably, it is not yet clear whether the ROV can deal with the complexity of mining projects and whether it can really be applied to make decisions that improve project value.
Naysayers will point to Windows 8 and Metro as the best OS available but, arguably, it's not yet available and isn't expected for months – if not years.
Darkest Dungeon (Linux, Mac, PlayStation 4 and Vita, Windows) Arguably, Darkest Dungeon is not yet officially out.
AMR has been high on the world health agenda for some time (though arguably not high enough) and yet global efforts have not moved forward fast enough.
That is, they might arguably mark time reference, but not yet systematically.
Even a company as massive as SalesForce has arguably not found its marketing scale yet.
