As to the whole "keeping the seat" warm issue.
Janeway is a canon character with 7 TV seasons of episodes and character exploration. It would be very difficult for a non - canon character introduced in the novels to EVER have the story potential that she does.
And yet other novel series have do just that and seem to be doing well. In fact I believe the whole relaunch thing was seen as feasible due to how well Star Trek: New Frontier, which had only a handful of canon characters in its cast was doing at the time.
besides the only difference between an non-canon and canon character is that one showed up on a TV series and the other didn't, big deal.
and now we can go back to the main characters - which is why we bought the book in the first place.
Speak for your self I like seeing new characters as it expands Star Trek instead of keeping it confined to the same groups of people. If Paramount and CBS had followed that logic Star Trek would have only consisted of TOS and its films.