I believe the decision to use or not use telnet is best left to the individual user. Some may not like it, and it is indeed insecure, but if we "outlaw" everything that is insecure or unreliable or "could" be a problem, we'd be left with hunks of metal, plastic, and silicon.
And should Mitel ever elect to completely remove telnet from SME, then I suspect the solution for those wanting telnet should be to not use SME, but rather to use a product that will allow them to work they way they want. Or, wait for the contrib module that reinstates telnet
