Note about System.import

[danez]

I was reading through the migration guide and noticed the section about System.import.
When reading it it sounds like System.import is already a thing and the new specified way of how to do dynamic loading, but it is not and probably never will be in its current form (see whatwg/loader#149, whatwg/loader#147 and https://github.com/tc39/proposal-dynamic-import).

I see that some users probably already use System.import and it's nice webpack supports the current spec, BUT It would probably be good to add a note that says that this is not a final specification and that it is very early stage and will be changing in future. I think users should be aware of that so that they can decide if they take the risk of a evolving and changing spec.

I also saw some other sections that said TODO document System.import which maybe should add the same.

[SpaceK33z]

See webpack/webpack#3413, support for import() will probably land in the next beta.

[bebraw]

Yeah, the current beta implements import(). System.import() can be considered deprecated now.

[prewk]

pull request #499 fixes the deprecated System.import stuff in the migration guide.

[bebraw]

Closing since #499 was merged.