I was worried when I saw this, but the very next bullet point is:

>Overhauled default grid system. Now uses percentage widths, padding, and box-sizing: border-box instead of pixel widths and margins. Nesting and offsets remain the same.

Which sounds like they are actually making everything fluid, and removing fixed widths. Perhaps a good thing, although border-box means no IE7 support.

They also removed all IE7 specific CSS hacks. IE7 will no longer be supported at all.

Obviously this is particular to each site's visitor demographics, but the only IE7-specific CSS my sites need would be something along the lines of:

    #ie-warning {
        display:none;
    }
    
    html.ie7 #ie-warning {
        display:block;
    }

That's bold but the right decision IMO.

same thoughts here - worried, then optimistic as it should actually be a more simple syntax to create nested grids - would be really nice if you'd be able to do a project wide removal of "-fluid" and it all just works the same

That should work just as you described it.

I thought border-box was pretty much how IE handled sizing anyways up until IE8.