At present (mid-May 2023), the UPC CMS appears to have difficulties handling the number of opt-out requests that are being submitted. This does not appear to be a great start for the new system:
First, while the number of opt-out requests appears to be substantial (and appears to grow significantly as June 2023 approaches), this type of request does normally not involve significant data amounts. This leaves one wondering how well equipped the CMS is to handle the potentially simultaneous submission of several voluminous briefs in UPC field operation from June 2023.
Second, the number of opt-out requests appears to illustrate that there are many applicants and patentees who, at least as of now, are not yet convinced by the new system.
On the bright side, applicants and patentees appear to be aware of the options provided by the new system, and appear to pro-actively take the steps they deem appropriate for their patent portfolio.