So, staying with Sony means you can get a new FF body cheaper, but then you're having to replace all your lenses anyway - I presume again, at a discount ? So it's a big hit financially whichever way you go ?
Personally, I would look at this 2 ways...
First from a financial aspect, what is it going to cost to replicate what you are after with Canon and Nikon compared to Sony - especially as you say you get a discount from Sony...(Oh and don't forget, you have to pay for IS in the lenses with Canon / Nikon, which can be more expensive)
Secondly and probably more importantly, I would try the other bodies out - you have used Sony and are obviously comfortable and happy with it, you need to see if the Canon / Nikon bodies suit you, do they feel okay, can you manage the button layout, what about the menu system, is there something they do which is better for you that the Sony doesn't - or the Sony does, that these don't...
And don't forget, the grass isn't always greener on the other side (esp on the dark side

)
Hope this is of help...