I'd say that's a valid position you can take. And the power of the SAP HANA platform is available to the ABAP world as well.
Having said that, the SAP HANA XS Engine is does not aim to replace the NetWeaver stack.
It's supposed to provide a light-weight alternative for developments where you can happily accept the lack of "cushioning" through the platform in exchange for a smaller landscape footprint and a more direct access to the data processing.
Not sure, why you say that you can't use pattern with JavaScript - maybe this link (google for more) might provide direction http://addyosmani.com/resources/essentialjsdesignpatterns/book/
Coming to your last point, the "enterprise-class" application: I'd say, again, depending on what you want to achieve, JavaScript is not per se the wrong choice.
Having said that, of course the NetWeaver stack provides solutions to a lot of problems that will occur in large-scale business applications out of the box.
So, in terms of productivity - especially when you already have an established workflow for ABAP in place - you will likely be better off with sticking to it; as long as you only want what the framework gives you.
Especially when you want to or have to provide more modern UIs, you might want to look into SAP UI5 and FIORI - and there you are back in JavaScript land.
My 2 cts.
Lars