Hi folks! (OP here) 
 
Thanks for the very helpful discussion.  FYI, I went ahead and spun up the 9800-CL, joined my AP to it, and converted it to Meraki.  Worked like a charm.   This was quite the welcome from the Meraki community!  
 
My story -- our small company of ~20 moves into our new building in two days (Mon).  One week before the move, I asked about Wifi, and was shown 3x Meraki MR42's the priors hadn't bothered pulling down, years ago.  I doubted we should, or even could, use them.  Choices were limited for getting new devices in time, so I ordered 9164s w/ 3-year Meraki license, to arrive on move-in day itself, but luck bestowed one a few days early.  It arrived Thu -- incompatible, with ~3 days to fix it.  
 
Official support channels just weren't gonna cover this, not in the time I had.  I was told to purchase 9800's, offered to migrate my DNA license to Meraki, offered to take back the Meraki license and sell me DNA instead, etc. 🙂 
 
THANKS to this group, that AP was installed and working today (Sat), and I still get Sunday off.    Respect!  🙂 
 
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IF you are reading this in search of help on this path, here's my steps (links are below). 
 
I ran the 9800-CL on Ubuntu on Dell laptop.  KVM/virt-manager via the qcow2 image and the "installing with linux bridge networking" script taken from Cisco 9800-CL install guide (links vvv).  Virtual bridge to connect the VM to the laptop GigE port to the AP via PoE switch.  Only place I got stuck was when I hadn't properly setup the 3x virbr as per the Cisco script, where you fill in <network name>, as I fumbled getting that working, it would fail in an install script loop, without really explaining what the issue was, at least for me.  To setup the WLC, I used the "Day 0 CLI Wizard" (link vv) because I like CLI, but at step ~6 where it says "you can do the rest in WebUI", I switched the webUI and didn't do anything except the bare minimum to add the AP, wait for it to connect, then switch to Meraki mode.  Cisco provides a 5-pager PDF (link vvv) on how to do it, once you have AP connected to WLC.  Give every step time, esp the switch to Meraki, it will reboot a few times.   Seemed like forever -- half hour? -- from clicking convert to having it show up on the Meraki cloud.  And ~1 day for a "country mismatch" warning to clear.   The hardest part for me was setting up networking such that the VM could see the AP, consider your comfort level in that area and/or budget time to iterate on it!!  🙂   (I spent ~1 hour on that, and 2-3 on the whole process) 
 
 
https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/9800-cloud/installation/b-c9800-cl-in...
 
https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/9800-cloud/installation/b-c9800-cl-in...
 
https://www.cisco.com/c/en/us/products/collateral/wireless/catalyst-9100ax-access-points/migrating-d...