From a technical point of view, this will work fine.
In terms of the support contract supporting the systems it was previously attached to, or will be attached to, you should contact your local NetApp account team to address any "true-up" needed. There is no "right to use" licensing required, but to be covered by the support arrangement, some transcation might be required.
Thank you for your response. One more clarification if you wouldn't mind. The DS4243 EOS with IOM3 modules is EOS in 3/2021, but with IOM6 modules will still be supported beyond that date (not announced yet?)
HWU is just confusing (maybe just to me) because under tne main DS4243 page it says EOS is 3/2021, but when you click on the modules link, it only shows IOM3 with that date, and no announced date for IOM6 or IOM12.
I'm just somewhat novice at how these conversions work.
I think I can understand where you're coming from. There's a couple of things to consider:
IOM3 in DS424 - Supported in ONTAP 7.3.2 through 9.1
IOM6 in DS424 - Supported in ONTAP 7.3.4 onwards
IOM12 in DS424 - Supported in ONTAP 9.0 onwards
IOM6 in DS224 - Supported in ONTAP 7.3.3 onwards
IOM12 in DS224 - Supported in ONTAP 9.0 onwards
Then, the drives need to be supported in ONTAP - there are minimum versions for DS424 drives, but at this time, no maximum versions.
Then, you need to be able to buy support contracts, which is commonly something admins want, but not totally required. Some older drives are not available to be covered by support contracts anymore, or will soon hit that time. In general - if the drives are attached to the system when its contract is renewed, and there is no EOS date for the drives, they will be covered while the system is under support, along with the shelf components.
With the DS424 shelves, there are only a handful of components other than the drives - the chassis, the power supplies (2 or 4), the IOMs and a module that holds the shelf ID, and the power supplies are by far the most common part to need to replace. So basically - they'll be supportable from both a contract and a software point of view for quite a while.
I hope this clarifies the various issues around it - please feel free to post any follow up questions.