Is it true that more and more scholars in relevant fields are at least entertaining the possibility the Jesus never really existed?
Depends on what you mean by "more and more." There aren't many who are (publicly) seriously doubtful over Jesus' existence, and even among those there are few (if any) who take a hard-line stance on it and say that Jesus definitely didn't exist. Richard Carrier only lists seven credentialed doubters in a blog post
Ehrman falsely claims in his book that there are no hyper-specialized historians of ancient Christianity who doubt the historicity of Jesus. So I named one: Arthur Droge, a sitting professor of early Christianity at UCSD.
And of those who do not meet Ehrman’s irrationally specific criteria but who are certainly qualified, we can now add Kurt Noll, a sitting professor of religion at Brandon University (as I already noted in my review of Is This Not the Carpenter) and Thomas Brodie, a retired professor of biblical studies (as I noted elsewhere). Combined with myself (Richard Carrier) and Robert Price, as fully qualified independent scholars, and Thomas Thompson, a retired professor of some renown, that is more than a handful of well-qualified scholars, all with doctorates in a relevant field, who are on record doubting the historicity of Jesus.
Most recently, Hector Avalos, a sitting professor of religion at Iowa State University, has also declared his agnosticism about historicity as well.
That makes seven fully qualified experts on the record, three of them sitting professors, plus two retired professors, and two independent scholars with full credentials. And there are no doubt many others who simply haven’t gone on the record. We also have sympathizers among mainstream experts who nevertheless endorse historicity but acknowledge we have a respectable point, like Philip Davies.
So, only a handful so far, but this skepticism was pretty much unheard of until recently (as far as I know), at least among experts. I wouldn't be surprised if it keeps rising, but I'm not expecting consensus to change anytime soon. I'm kind of hoping this lights a fire under the pro-historicity academics to put a little more elbow grease into their defenses; too many of them seem to just want to fold their arms and talk about how this has never seriously
been doubted and that the consensus is so overwhelming that they shouldn't even be bothered with a few crackpots on the fringe.