I don't think you can do an Ocean racer smaller than the Mini6.50 not on account of the boat but on account of seaworthiness and safety. You have some guys doing the Pogo 2 in America and the boat is not expensive for an Ocean racer.
The last time I looked, the pricing on the Open Sailing Pogo 2's built in Los Angeles was about $100K / €75K ex-sails and electronics. Obviously used boats can be had for as little as $35K / €25K if you start looking at Pogo 1's or other older Series boats. And agree that it's not a lot of money for a bonafide ocean racing boat.
But if the Open 16 concept proves successful in handling a roundtrip Atlantic crossing in winter, and the price could come in near the low end of used Mini 6.50's, I think they could be viable for entry level offshore solo racing. Perhaps not for a Transat or even a Hawaii race (though Transpac and Pacific Cup weather is typically quite benign, by Atlantic standards - or even Bay of Biscay). For example, perfect for a Bermuda 1-2 and similar. And the cost of ownership for a 16ft boat is definitely going to be lower than for a 21ft boat, as well as being easier to transport.
Anyway, I've seen enough of these project to not get my hopes up that anything will come of it, aside from the materials technology aspects, which are probably the most important parts, in this case.
Fortunately, the actual Mini Transat has finally started, and the Proto favorites jumped immediately to the front, as expected. Boidevezi was leading Pedote by a small margin, last time I looked, with Marie, Gahinet and Sugre in hot pursuit. Haven't consulted the metéo yet, but probably only a matter of time before Pedote disappears into the distance.
Just as Macif will do within the next 24-48 hours, notwithstanding the charging Stamm (now leading) or tenacious Riou/Le Cam or Paulo's favorites, Guillemot/Bidégorry (who are 50 miles back of Gabart/MichDesj and 75 behind Stamm/Legros).
Speaking of Stamm, I really believe that if he'd had his boat sorted for the last Vendée Globe he would have given the two VPLP boats a much closer challenge. It was clear within the first week or so that his JuanK boat was not ready to race, and he ended up breaking things by having to push hard to compensate - even little things like his coffee grinder winch failing, caused big problems. And, of course, the charging system. But that's part of the game: Macif and Banque Pop were totally sorted, having benefited from the incredible support teams built around both boats, and training together for so long. Now that Stamm seems to have his boat in order - and his health - we are seeing why he is a man be be reckoned with. Probably not many faster in an IMOCA 60 - indeed, perhaps only Gabart, Desjoyeux and Le Cleac'h.
Finally, as to the misfortune of the Ker Class 40 Concise 18, another case of a boat not fully sorted, having arrived from the yard only a few months earlier and never having been put to the test in these kinds of conditions. In this case, their retirement appears to be related to rudder failure, but unclear whether they struck something or if it was structural - i.e., stress failure, etc. Looking forward to reading more on their web site. My guess is that Jason Ker will figure this out, eventually, if he wants to. Sam Manuard, on the other hand, has years and years of first-hand experience how to design fast shorthanded ocean racing boats, so no surprise that his designs are dominating now - I mean, really, really dominating - as in they are in a completely different class of performance, it seems.