OK it's now been confirmed that the new ผ.60 (ผ.60-ผ.17) exempt entry stamps are not subject to the "old rule" of two entries by land/sea borders in a calendar year.
This means that the stamps are available for "unlimited" entries by visa exempt via land or sea, exactly as they would be entering by air.
I use quotes around unlimited because that doesn't mean you can use them over and over and over again, just that there is no set limit on the number of entries you could potentially get. All entries are subject to the individual Immigration Officer you give your passport to. If that officer decides that you are trying to milk the system then they may question you or just flat out deny entry.
With the old "2 entries per year" rule you were pretty much "guaranteed" entry 2 times after Jan 1st, even if you'd had a fairly extensive history in the year prior.
The ผ.60 stamp is too new to work out if there may be issues related to that going forward. We shall have to wait and see how it pans out.
TLDR : Answer Summary
The newly confirmed ผ.60 entry stamp allows for unlimited visa-exempt entries into Thailand by land or sea, similarly to air entries. However, this doesn't guarantee repeated entries, as each one is still subject to the discretion of the Immigration Officer. Previously, there was a limit of two entries per year under the old rule, but the new rule poses potential uncertainties as it is too new to predict any future complications.
