I don't know when the planned start date is. I think they may have made an announcement a while ago about enforcing the limit on SOAP, which they did not do before, but I am not 100% sure when that would have gone out publicly.
Might be a good question to ask your CAM; they can confirm with product management.
It's not in the release notes so I hope it hasn't been rolled out.
Please understand this is a major breaking change. Unless you have your REST and SOAP calls going through the same mediator or queue, which was not previously necessary, you will not be able to coordinate usage across your connected apps (previously, you only needed to coordinate REST apps with other REST apps and SOAP with other SOAP). Now, you'll have to set a false limit on one or the other or rearchitect. It's hard to not to see this as a step back -- unlike, for example, upping the total to 15,000 shared calls, which could be viewed as an improvement.
I do understand that, as it impacts my customers as well. I know product management has been made aware by that previously, customers were told it was separate so changes will likely be necessary for at least a subset. I think there may be plans to reach out individually to customers who are going to be impacted based on their current volume, but I don't know for sure. I think your CAM is the proper person to take this forward; I don't have any influence over those kinds of decisions and I don't know what the plans are for rolling this change out.