I don't see why this wouldn't be possible as long as your STP design supported this topology. I.e MS320 (A1) as the root bridge and port costs, speed links etc would ensure that the STP topology would match your intended design. I.e The Meraki switches would just put the "highest cost" ports to the root bridge in a discarding state until a change in the topology was noticed. Meraki switches support STP/RSTP.
What other branded switches are you using for C2 and D2, do these support STP/RSTP and what speeds are the ports on these switches?
It would be great to also know what interfaces/ports on the switches that you would use for the re-redundant and primary links for each switch.
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On the whole, I would change your design. You don't want links between access blocks. Given you diagram, you are probably best having a collapsed core-distribution switch (or switch stack for redundancy). You should then dual connect each access block to the collapsed core.