Season 3 is definitely happening with the old cast and crew. And not only are they filming in Iceland, DIS will be (right after the Picard show) their major attraction for Comic Con. Where they booked the f-in main hall for Star Trek. Remember when they last time booked hall H for Star Trek? Yeah, me neither.
Now let me put it this way: The market today is extremely different than in the 90s or 00s. DIS' has miniscule audience numbers compared to previous Trek shows (even ENT), and less than "The Orville" on television. But those people are directly paying. Not through advertisement. But directly cash in the hand.
Now, all streaming tv IMO is currently jsut a giant money-dump. That includes Netflix and Disney+. Right now, they're investing, investing, investing, in hope for future returns.And CBS is in that game, and commited.
If I had to make a personal prediction: DIS season 3 will be the last one. But not in a "surprise cancelled" way. They will phase it out with a plan, and a big bang at the end. I guess the show hasn't been the success they hoped for - they're betting on the Picard show for their golden goose now, because it's new, and exciting, and they're going all in for that, with posters, a Comic Con appereance and a really big frikkin' marketing campaign. DIS will be the one "also on" show, to sell the service as more than one show, but a universe. And they're intent to go out in style, probably with a direct replacement (S31, Pike, or both) as a follow up. And I personally guess the Picard show will be planned as a 3-season thing right from the start. I doubt we will see a 7-season series anytime soon again - except if they introduce a new "flagship show" with a big crew set on a single ship (probably after PIC has already ended though). But 3 seasons seems much more managable for a streaming service. Also, Stewart only commited to 3 seasons on TNG(!) (that's why they kept their options open with the cliffhanger in "Best of both worlds"). No way he signed on for 7(!) seasons at his age. The future is probably more, but a lot shorter series, with new series every few years that take over elements from previous short series.