We should at least implement basic features that some programs depend on. That should include wrapping functions around an open-source solution such as Mozilla.
It is also my opinion that we should not force Internet capabilities if people do not want them. This was (and is) Microsoft's biggest mistake, especially with Windows 98. I know many people who think that Windows 98 shouldn't have had Internet Explorer. they continued to do it to Windows NT at the same time (Windows 2000, as it is commonly called). Microsoft pushed it even further in Windows XP, making the activation feature (oh please. DO NOT copy this) in JavaScript. They did it mostly so that people who removed Internet Explorer from Windows forcefully wouldn't be able to use Windows XP. (One more common work-around is to illegally download the Corporate edition.)
If you feel it to be necessary to copy some basic Internet Explorer features that are "integrated" into Windows, go ahead and do it. Please, however, make it optional. I guarentee that if you do not, someone will derive from the official project. People make derivation of the proprietary Microsoft Windows (98lite, nLite, vorck.com/remove-ie.html), ReactOS is much easier to modify.