Clone or feedback loop in transporter holding his equivalent. Hollow deck A.I. that’s an exact copy from matter replicator image of his mind. I don’t know why you would want that fucker back though.
You could extract a copy of Kirk from the Nexus.
An alternate version of Kirk comes from an parallel universe.
Evil Kirk could cross over from the Mirror Universe.
Someone could create a sentient hologram, or an android, of Kirk.
Considering that Shatner is now 91 years old, and not exactly in the best of health, the prospects of any script with him as integral to the plot are worse than slim. Consider the time it takes for a movie or series to go from conception through to completion. Then ask yourself who might risk their money financing a project with one of the principal roles slated to a man virtually chained to the angel of death? Would you risk your money on Bill being available at the onset of production, let alone withstanding the rigors of the process once begun. I suppose he could be portrayed as appearing comatose in a futuristic process where he appears dead but his mind remains agile. The plot might then consist of flashbacks on dynamic events in the life of the dashing hero played by a younger actor.