This is just going to be a quick rundown on my thoughts for Mini-Dex: Stormtroopers.
The Scions are fantastic. Definitely going to get some of these and with something like 17 heads in the box for 5 guys there will be spares to put on my existing, badly painted guardsmen.
The Taurox next. Almost everyone has said "it's crap" or some variation of that. I disagree. I think the overuse of heraldry and horrible colour scheme GW chose make it look worse than it is. With very minor work these things could look much better (just look at my stormraven for example, very simple conversion).
Only had a quick glance at the rules in White Dwarf but I like them. Basically they are Stormtroopers but in small platoons and without the spec ops rule (but have deepstrike and move through cover, 2/3 spec ops options, as standard). Most importantly though is that they may First Rank Fire, Second Rank Fire with their HOTSHOT LASGUNS!!!!! ABOUT TIME!!!!
Taurox is not bad for the points. 50 base with the option to take different weapons. 11/10/10 so not very tough but a razorback is only 5 points less base and can only carry 6 people compared to the Taurox's 10. I can see my command squad's one of these being my AT-AT quite easily.
So what does this mean for the IG themselves? I can easily see Stormtroopers coming out of the main book and slotted in as allies specifically from this book. It would be a shame but it makes sense not only for profit but for fluff too. Stormtroopers are not part of the main IG army, they are placed in as-needed. Just like (with very few exceptions) Valkyries are not part of a guard army, they are part of the Navy and loaned to the Guard.