Just waiting on you to free it, even if there was a promised (but not in the license) deadline to do so is a lot legally shakier, you'd have to pursue it under promissory estoppel.
Such a licensed application would change its "main developer" over the years, for example someone would take the 4 years old free-beer version, invest money and time and create a compelling feature set that would make people pay for their version, after 4 more years someone else could do the same to the new feature set etc. So while the initial developer has the freedom to release under multiple-licenses, once they go for "commercial-copy-left" they set in motion a chain that restrict what future developers can do, forcing them to release their work too as commercial-copy-left if they want to have the 3 year binary exclusivity period.