No competent manager would undertake a rewrite without new functional requirements at hand. Feature parity may well be the first milestone, but without an idea of what future projects might be, it's impossible to choose the best tools to facilitate them. Commercial companies are there to serve customers, make a living for employees and generate returns for owners/shareholders, not for funsies, save that for a hobby github project. Any managers not willing to listen to engineering concerns / articulate their own and any coworkers who expect others at work to be happy about every single aspect of their employment need help.