... an option that has been available in both previous Dragon Age sequels which would be reasonable to expect in the next game.
Yes both sequels (presumably Awakening and DA2?) supported offline imports. And in both cases, that option came with bugs, missing flags, and broken plot points (sacrificed Wardens in Awakening, for example). Bioware could have provided the same option, with the same effectively unfixable bugs for DAI, locking out cross-platform players in the process, along with anyone who had lost their savegames, and denying new players the option to create a world state.
Instead, they chose not to continue with that particular method of importing, and instead created a solution allowing for cross-platform, validated, persistent world-state imports, for new and old players alike, supporting the next DA game along with media that's yet to exist in the DA series. Yes, this solution locks out players who either can't or won't connect their gaming machines to the internet (though "won't", as mentioned, is not Bioware's problem), but when you consider everything the Keep offers which simply would not have been possible under the old system, it's clear that the old method was untenable.
As for an offline option for the Keep itself - as mentioned, that comes down to resources (cost and time). It's obviously not a five-minute job, so the question has to be asked - does this offer enough value to the player base to justify doing it, and absorbing the additional support requirements for that process, now and in the future? Bioware have mentioned a few times that they're still looking into it, so presumably it hasn't (yet) been ruled out. Maybe something will be arranged, and if so that's great - an extra option for those players who need it, and irrelevant for those who don't (like the bunnies).