I absolutely believe that they tried round bases. Again, they really should have tried everything, including just straight up 'fantasy, but with 40k rules'.
If they go to a skirmish game, then round bases absolutely make sense. Even for a battle game, round bases could be fine for single model units under certain conditions (facing doesn't matter, combats are unit to unit rather than model to model). If they want units to rank up, then round bases are less good, of course.
The important things, IMO, for new fantasy are as follows:
1) buy in cost is low. This means the game must scale down, and must be a good game when scaled down. I do not feel fantasy achieves this currently. At the very least, small games need to work as well as they do in 40k. GW wants to sell 'premium' models for 'premium' prices, and honestly that is absolutely fine, but the model count per standard game needs to come way way down. It's not even just the price, in games of hundreds of models on a side, GW's fancy models take too long to paint, and the fancy details of individual models are lost in the crowd.
2) 1 box = 1 unit, with very few if any exceptions. The standard unit sizes in fantasy these days are often 2 to 4 boxes. That's gotta stop.
3) Manageable stock. On the one hand, cutting way back on stock will really tick off their existing stockists. On the other hand, bunches of places don't stock fantasy because there's just too many factions with too much junk. If they're starting fresh, they should actually do that. Few factions, few units, manageable stock.
4) The game is good. I know Najo's got a ton of confidence here, but I'm a bit more skeptical of some of their recent ventures. They need to go smaller scale if they want to keep selling premium models, but there are a lot of really good smaller scale fantasy mins games. Games that can be played in an hour. Games that are satisfying both casually and competitively.
5) Community support. They're effectively relaunching what they would like to be one of their flagship lines. The existing community of players and retailers, what of it hasn't already drifted away, will be in some large part alienated by the change over. They need to get new blood excited. Posters, giveaways, promotional models, web content that isn't just a store front. If not tournament support then support for leagues and narrative campaigns, GW reps who can travel to retailers in places they don't have stores to talk up the game to skeptical owners and run demos for interested players. More of their already pretty damn quality 'how to paint' videos. Battle Report videos between developers featuring game mechanics they like in the new edition. Video interviews where the designers talk up the fluff, look, and gameplay features of each of the new factions, sort of like how the League of Legends folks do for new champions.
The absolute ideal would be a sort of 'tale of X gamer' (with x = the number of factions in 9th) escalation league article series running through several months of white dwarf, featuring key design studio people (rules designers, sculptors, heavy metal painters), with those same people appearing in video battle reports using these new armies on GW's youtube page and in design interviews about the new game as described above. Throw in some unique scenarios in their campaign, and a stapleback campaign book including some of those scenarios, fluff info, faction descriptions, and minimal rules + statlines for the smallest starting size to be given out as a free promotional thing to let people try out the basics of the new game for themselves.
A bunch of those booklets would go free to any store that stocks enough of the new range, along with league support - escalation league info (unique scenarios for games of each size), and prize support (game counters, promotional dice, etc). Make it a big thing. Make a larger point of featuring individual stores and gamers participating online and in white dwarf.
I don't know. Whatever they do, they need to establish at least the aura of interaction between GW and the community. They need to break this impression of the withdrawn corporate body up in their ivory tower, releasing games without caring if anyone likes or buys them.