"I've seen Fleetwood Mac many times. Quite a few times early on and several times here recently.

ALWAYS a fantastic show!

The band Fleetwood Mac has always had a tumultuous history. Why would this be such big news?

Seems to me the new dudes are quite accomplished and should be a worthwhile addition(s) to the band.

Love Lindsey, but time marches on..."

100% ditto here. I've seen them once... It was 2013 or 14, prior to Christine rejoining the band. All the greats are getting older, as are some of us. As much as I enjoy Lindsay in FM, I would be open minded to see the upcoming tour with Mike and Neil. Thanks for the recommendation for FUTURE GAMES. I am just now delving in to some older Mac I now have as part of an LP collection I recently bought. I have been enjoying Then Play On, and will likely reach for FG next. 
I would think it could be weird for Neil and Mike to sing and play Lindsey's parts, and even just to be in Fleetwood Mac. It's not that much different to being in a Fleetwood Mac tribute band! Neil's a fine songwriter, and now he'll be performing someone else's compositions. I wonder if the gig is just for touring, or if Neil and Mike are permanent members and will be recording new material with the group. Fleetwood Mac's fourth incarnation?! Or is it the fifth? Still my favorite lineup is that of the Kiln House album era. For guitar players it's the original, Peter Green lead version. I have been wondering what Mike Campbell would do post-Petty, and now have the answer.
Of course I was a HUGE fan of the Buckingham/Nicks era Fleetwood Mac, but recently went back to revisit the early stuff.  I'm not a fan of the first three albums, but from Kiln House (1970) to Future Games (1971) to Bare Trees (1972) to Penguin (1973) to Mystery To Me (1973) to finally Heroes Are Hard To Find (1974) these albums are pretty incredible.

IMHO, these era albums are overlooked/underappreciated because they weren't big commercial successes like the later works. 
I'm a fan of the original four (and later five) piece band with Peter Green, Jeremy Spencer and Danny Kirwan on guitars.  That band had an amazing sound.  I sometimes hear traces of it in the music of Los Lobos and ZZ Top.  Lots of talented musicians came after Peter Green left but I don't have much interest in what they did.  It is interesting that the name survives--the music is so very different.
I'm firmly planted in the Peter Green incarnation. But it's amazing that they've been through so many transformations, most of them very, very good, and that they continue today!