I'd go further and have BasePage.getRedirectTarget() return an object of the same class as the redirect. This would keep the implementation general and allow other subclasses that want the returned object to be the same class to use the method without overriding it.

It could be implemented in BasePage.getRedirectTarget() or Site.getredirtarget().

def getRedirectTarget(self):
    target = self.site.getredirtarget(self)
    try:
        target = self.__class__(target)
    except ValueError:
        pass
    return target

What about internamespace redirects?

Change 538378 had a related patch set uploaded (by Xqt; owner: Xqt):
[pywikibot/core@master] [IMPR] Upcast getRedirectTarget result

https://gerrit.wikimedia.org/r/538378

In T233392#5512600, @Dvorapa wrote:

What about internamespace redirects?

Currently a InterwikiRedirectPage exception will be raised

Change 538378 merged by jenkins-bot:
[pywikibot/core@master] [IMPR] Upcast getRedirectTarget result

https://gerrit.wikimedia.org/r/538378

In T233392#5512600, @Dvorapa wrote:

What about internamespace redirects?

These are not affected by Xqt's patch - you just get the right class according to the class, which I think is good - if you expect a Page, you can still use it as such, if not, you use it according to the expected type.