I was able to replace the failed HDD with a new hybrid drive and install Mac OS Sierra Beta without a hitch.
I wanted to try a straight-up SSD, but cost per GB hits me in the cheap spots. I looked at a regular laptop HDD, but for just a couple dollars more I was able to get a fhybrid in the form of a ull TB with a SSD front. I can't tell from the box or drive utilities how big the SSD is, but I figured it can't be any worse than a straight HDD.
It took just a few minutes to remove the screws, swap the drives, and replace the screws. I booted the MBP to the network restore utility (pretty neat-o, Apple) and attempt to restore from my Time Machine. I had skipped partitioning the drive, hoping the restore process might do that or offer to help, but it didn't. I poked around a little bit to try to find how to ensure there's a restore partition, but there aren't the right Google terms to find how to create one--plenty tell how to identify one, though. I let it go figuring worst case I do the network restore again. WIth the disk partitioned as one giant journaled partition, I gave the restore a try again.
It said it would take about four hours, but it took only three hours and fifty-five minutes. The restore finished while I was away (didn't sit there to watch), and my normal destop was waiting for me. I rebooted to make sure it was running off a fresh boot and not the restore process. Judging by my expectations, it seemed pretty fast, although in all fairness I didn't restart the system very often. It immediately had some updates, and I ran through starting my normal bits of software and doing some of those updates, too.
Then I moved the MBP and heard the rattling. I glanced at the removed original drive and face-palmed myself because I'd forgotten to move the stubby bits that go where the screws would be used if mounting it elsewise. A quick off and on again with the back panel and the new drive is securely mounted in the place of the old.
So far there's nothing jumping out as a problem. I've not taken any time to evaluate any of the new features, except a quick poke at the Siri icon on the menu bar. I hope to do something fun and different in the coming days, 'though I probably won't write about it unless it's a stellar experience.