I am against constrained DSLs in general unless it buys you something. In the general case, with a DSL you sacrifice expressivity in order to gain security guarantees or improved performance. In this case you are sacrificing expressivity to gain performance but I don't think the performance gains are meaningful enough to be worth sacrificing all of that expressivity. So to answer your question, I am generally opposed to constrained templating DSLs for web frontend applications overall.