This was started just under a year ago so you could have signed up and filed 2022 1099s via IRIS (and currently that's all it does, despite there being 2023 1099 forms that you can download and/or order from the IRS right now, they don't have the IRIS schema defined for 2023 yet).  I discussed it with my clients late last year and all agreed not to be the guinea pigs for a brand new system.

The IRS had a session on IRIS at the Nationwide Tax Forum.  IMO the system is not ready for prime-time and not designed with tax professionals in mind.  With that said, they are starting with something small (because it was mandated by Congress) and making improvements as they go.  I think the long-term plan is to replace (or at the very least merge with) the current FIRE system.  The system will need to be significantly more robust before that can happen.

If you have clients who either prepare their own 1099s or use one of the online services, they may consider switching to IRIS for the TY2023 filing season.  If you can survive the registration process, it's geared towards small businesses (and IMO, that's a great place to start!)  Each employer will create their own account (tied to their EIN) and be able to enter/submit 1099s as well as print recipient copies.  If the employer is used to using a service that either does the recipient stuffing/mailing for them or even better has online download capability for recipients, IRIS is no match for that level of service.  It's a glorified typewriter that's supposedly generous enough to remember your entries from last year.

Tax professionals do have the ability to sign up as a transmitter for clients.  This is done via your existing eServices account.  The glitch I ran into was that I had to dig out my SS-4 letter because my business name had to match exactly what was on file for my EIN.  Once I got through the application process, it was approved within the week (I think 2-3 days).  I have signed up but not submitted anything.  My objective was to survive the registration process and then decide whether or not I want to use this in January.  If nothing else, I'll personally be the guinea pig and file a nominee 1099-INT for a joint-account holder.  The problem I see for tax professionals (and for large businesses) is that the upload files (fairly convenient if you are or have an Excel wizard around) are limited to 100 entries per file.  Also, preparers are limited to a fairly low number of clients.  I don't remember the number and can't find it online right now but my recollection is that the limit is a double-digit number.  So if you have 20 clients for whom you submit 1099s, no problem.  If you have 200 clients IRIS is not the solution for you (at least not yet).

Rick