Having overhead racks which can actually be used for real luggage was part of the design specification for the IETs. Seems harsh to criticise Lumo for basically doing what the dft recommended, just the same as all the other operators with the stock.
A minor redesign would help, putting a small lip of a few inches at the edge so lateral force doesn't cause stuff to fall off. Probably be quite easy to bolt something on. I do like that bigger stuff fits up there but it isn't well restrained.
i personally find the much better choice of seats in Lumo much more important than luggage provision, and I'd far rather they invested in platform staff to enforce their sensible luggage rules than cut back on the space dedicated to people
Sensible if you're going for a weekend city break or a two day business trip, useless otherwise (unless you're a super light packer). As a low-cost operator I'd consider it reasonable for them to charge for larger bags like airlines do, but they simply don't offer that service at all. The size is very slightly bigger than airline hand luggage, but it's not big enough for me (2XL size clothes) for a week, and is utterly useless for any kind of outdoor activity type trips unless you're one of those people so obsessed with small-and-light that you cut the handle off your toothbrush.
Twenty quid for a full size piece of hold luggage would motivate people not to take bigger bags while providing for people who need to. Though that said I suspect if the issue was it falling on people that hard-sided bags of whatever size were more of an issue than physical size, particularly as a lot of larger camping type stuff is quite light and soft, e.g. modern lightweight tentage and sleeping bags - being clouted round the head by a hand luggage sized metal sided flight case would be a lot more harmful than a soft but large camping rucksack. Hard-sided bags are also more likely to slide off - soft bags might be more "squashed in" if large.
(I wouldn't like to see that on the proper railway, though, they need to make proper provision as part of the deal)