Though Sean Patrick Flanery states quite clearly that there is no Indiana Jones without Ford, Flanery has portrayed the character before in The Young Indiana Jones Chronicles.
But having said that, I mean, to me, Harrison Ford is Indiana Jones.
Airing on ABC from March 4, 1992, to July 24, 1993, The Young Indiana Jones Chronicles explores the childhood and youthful adventures of the beloved character, with George Hall playing an elderly version of Jones for the bookends of most episodes, though the show was able to obtain the talents of Harrison Ford to bookend one episode.
While we do not yet know who, if anyone, from previous installments in the franchise will appear, one actor who would relish the opportunity is The Young Indiana Jones Chronicles star Sean Patrick Flanery.