As a software developer myself, I understand that SE did not want to spend resources touching old content. Changing it to a solo instance is a very good idea but it would require quite a lot of work, much more than what they have done which is, basically, change a "false" for a "true", or a "0" for a "1".

However I think it will punish heavily the new players with extremely long queues. And once they are in, maybe some of them have not had the chance to upgrade their gear properly which, if you consider everything, could convert it into a real nightmare especially if there are not many veteran players in the party.

Before the change I queued occasionally. After it I know I will not queue ever again for it.