My point is that deferred or async loading of a script is part of the design of that script. Inflicting deferred or async loading on a script not designed for it is likely to have bad consequences.

If this is important to you please consider proposing and implementing a pull request for the DNN core that properly implements the feature and allows developers/designers access to the correct choice for their scripts. If there is general interest in the feature you will likely find people who want to work with you on it.

and in the dnn world it would be trial and error to implement large scale asynchronous calls in the loading of css and js files as an ad-hoc exercise. there are a lot of fish swimming in the pond. but i am not averse to exploring.

to the larger point, fast page loading should be of interest to nearly anyone running a commercial sight or who plans to use, let's say, google ad words to advertise. google punishes mercilessly slow pages. if dnn implemented an asynchronous loading strategy, or made it configurable, and it had a material impact on page loads, then it should be in dnn's interest to pursue  it. it may not be as simple as all that.

however, i made sufficient progress by implementing client resource management. desktop results are in the 90s and mobile in the 60s. that is good enough now.