Switch from a99ii to a7 iv?

The A99II can do 12 FPS, right? The A7IV can only do 10 FPS. The A7IV has less pixels too. Maybe you meant the A7RIV? Still only 10 FPS.

Higher pixel count? The A7iv is 33MP, the A99ii is 42MP.

The A7iv looks like a very good camera, I'm quite tempted myself, but pixel count is a downside for me. Yes, I know 24MP is plenty really, but I have got used to the cropping capability of 42MP.

Or did you mean the 61MP A7Riv?

A lot of the attraction to me is the LA-EA5, which makes the A1, A7iv and A7Riv viable alternatives to the A99ii. Not that the A1 will be in my price range for a decade or so.

I do find myself attracted to several E mount lenses (I even kid myself that the FE 200-600 would make me a bird photographer). The problem to me is always price.   

I totally agree with you Addy. Steve why selling a pristine A99 ii (and a beast of a camera) for something with almost the same specs???
Ask yourself if there are pictures you could not have made with the A99 ii and you could with a A7iv. I don't think there are.
I wish I had a camera like the A99 ii.

You say your considering the change for a smaller lighter form factor of a system while using your existing A mount lenses via the LA-EA5 ?

In which case your lenses are the same and with the camera attached to a lens , there's very little difference as a combined unit .
Your camera bag will be no smaller or lighter .

If you were after changing lenses as well , that's a different question .

If it still works for you , I'd stick with what you have .

I hesitate to comment on this question, having neither of the cameras discussed, but I would tentatively suggest keeping the A99 and getting one of the smaller-form-factor APS-C E mount cameras as an addition. The A6300/6400/etc have most of the useful capabilities of the FE cameras and enough Mp for most uses too.

I don't want to start the whole format-war thing again, but with modern sensors I am far from convinced that FF/APS-C makes much difference except in extreme uses I don't personally do, but you still have the A99ii for these ...

I use both the A7rii and A6300 turn and turn about (they have similar menus and controls) and I'm hard pushed to tell the pictures apart unless I crop very heavily, and the features aren't that much different either. The A6300 + 18-135mm OSS lens (my new favourite camera/lens combination for general use) gives very similar results to an FE camera with 28-200mm, but the whole thing is usefully smaller and lighter (and cheaper).

Just my 2p worth anyway.