You misunderstand the situation, XC has no intention of being permanently closed-source. The Rev1 mixer code has already been released, and code will continue to be released on a delayed timeline as new Rev's come out.
Bitcoin doesn't delay release of its code and instead makes sure that it is thoroughly reviewed by the entire world before incorporating anything new into the official version. Monero does the same.
The "delayed timeline" approach reeks of insecurity (in both compsec and psych sense of the word).
Imitation is the sincerest form of flattery and should be welcomed as a key form of validation, not avoided.
Only a total newb would accept obscurity as a form of security and source of value.