to me, the single greatest failure of the GW's WFB and 40K, aside from the dreary IGO-UGO turn sequence, is that their list system allows you to basically make the game a contest between who picks the best list. So the skill contest in a typical GW game is based on two things:
1 - can I make a list (using numerous cheesy options) that you can't beat,
2 - Can I afford to put it together in some way or another?
The actual skill level of play for 90% of WFB and 40K players has nothing to do with their ability to play the game well. It is based upon their ability to model a dozen obscure units and unit combinations and then surprise you on the table with various combos of magic items and characters. So it is essentially an arms race - very good for GW sales.
Point of comparison:
When you play Warhammer Ancient Battles (the historical WFB game), every list I know requires you to take minimum 50% Common (Core), MAX 25% Uncommon (Specials and Rares) and MAX 33% characters (Heroes). Note that is in POINTS VALUE. So you field a 2000 point army, 1000 points MUST be Common troops of that historical army.
In WFB, you can take just three UNITS of core, and FOUR specials and TWO rares and the rest in characters. For a 2000 point Empire army (based on Renaissance Germany), that can be as little as 150 points of troops (3x50pt units), or 7.5% of the army total points.
So what is the lesson? That when GW considers 'history', 50% of your army points are spent on common troops. When they consider Fantasy, 7.5% of your troops must be core troops. So the system they set up, including the category names (what do the names mean when you can have 2x specials and rares than core choices?), actually has no meaning.
The 'Nid evolotuionary program is just another variation on the same theme, to wit, "How can I develop an army to surprise, shock and stun my opponant and win all the time without really learning how to play the game well?"
So my final point is "I would hate to see Mongoose go down the same path". Although GW's game system provokes 'Arms Races' between competitive players, requiring you to buy lots of new models and model lots of unusual specials, rares and Dogs of war choices, which is good for their sales, as a system of gaming, it stinks unless you can come to some sort of gentleman's agreement with your friends.
I think that there is plenty of flexibility with the present mongoose troops choices and lists, and welcome the opportunity to try various combinations of stuff as they are released.