I like the idea of opening on the last scene of the TFA and connecting that with the opening of the Last Jedi. My idea would be to rescore the music of when she sees him and have her walk up to him, then pull out the lightsaber when she’s closer, she holds it out, Luke looks at her (using a shot from TFA), and then he just walks past her. With the right editing and musical rescoring, it could be very powerful.

The only issue is that you would need a crawl explaining that the Resistance has fled their base and is being chased by the First Order, which wouldn’t be hard. But someone skilled in special effects would have to create an opening shot after you pan down from the crawl showing Ach-To and THEN you would cut to the Millennium Falcon jumping out of hyperspace and them arriving (assuming you use a TFA ending like DigiMod’s).