I believe the ability to use React and Vue within the ServiceNow platform outside of Service Portal is there. Simple and straightforward, though are terms that depend on a personal point of view. I think that it's a simple and straightforward setup, the same as AngularJS was (and still is) before Service Portal came along.
With that said, once an application starts getting complex whether within the ServiceNow platform or outside standalone, it isn't "simple" or straightforward any longer. A bit more organized maybe but definitely not simple or straightforward.
Example below I setup two pages; one using a UI Page and the other using a Processor but both using the same UI script. It took me a little under an hour and the majority of it was figuring out how React worked because I've never used React before. But I felt putting it into ServiceNow was simple and straightforward.
The pages have the "Getting started" example of placing a button component on the page and a list component. The list component is using a
fetch to the API table to get the users.
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I think if someone wanted to, it would already be possible to create an application like Service Portal but allowing the use of React or Vue instead of AngularJS today.
You're absolutely correct, it's already there. We definitely can use modern web frameworks in ServiceNow. It's just almost every day I see how people are struggling with Service Portal because of proprietary API, angularjs, IDE etc.
Service Portal works fantastic for simple tasks with minimal configuration, but some advanced functionality makes things exponentially complicated in Service Portal.
