1. Doctor Who has been historically defined by change, but this does not mean that radical change will be successful today.
But what, exactly, is changing? We have a Doctor, we have a companion, we have a TARDIS. The audience is already used to the idea that the Doctor can
change, and they know that companions come and go. The only thing that is really different from the past five years is the writers and producers behind the scenes, and is that something that the core audience, not fandom, will really note?
2. Even if major change is helpful, that doesn't mean that several major changes all at once won't be too much for the audience.
But on screen, there aren't that
many changes. New Doctor, new companion, new TARDIS. And each of those changes are going to be explained for the audience. We have a regeneration. We have the TARDIS heavily damaged. Why would the audience find these things alienating?
After all, nuWho has been fairly stable since David Tennant assumed the role; there is the possibility that too much major change might hurt the series today and lead to its cancellation.
But as I said above, Sci
, nuWho isn't synonymous with the Davies/Tennant era anymore.
I'm not saying it's likely -- I'm just saying, bear in mind that what worked 20 years ago is not guaranteed to work today.
It wasn't guaranteed to work twenty years ago, either.
At this point, I don't see that the change from Tennat to Smith will be as radical or as traumatic as the change from Troughton to Pertwee. Pertwee's Doctor Who
might as well have been a different series entirely. Smith's Who
doesn't appear to be as radical a departure from the past.
At least, not yet.