Obviously this is a long, long way from a functional brain being grown. But I have to wonder where the moral line is drawn when you're talking about growing an organ that (may-or-may-not) hold the ability to form a level of consciousness.
The quick answer is to say it's not ethical. But what if the brain is given full autonomy and ability to communicate with others and then let the brain decide if it wants an organic or machine body?
So what you're saying is we should take anything with a brain, figure out what it's answer would be to "do you want to be alive ?" and then support that decision ?
Boy, you must hate abortion ...
(just saying that those things obviously have a brain, and every last kid on the planet will say they want to be alive, so those embryos being aborted can be easily assumed to either be conscious or at least said to be rapidly becoming conscious, and we can be likewise sure they want to be alive as well. Human embryos have functional brains 20 days after conception, which is just barely after a woman would become aware of a pregnancy, and we support abortion up to 6 months or even later, at which point a human embryo has a brain with more functional neurons than almost any animal on the planet, and more than every dog, cat, primate, dolphin)
(and just to defend this research, any research that gets us closer to being able to grow specific tissues - especially neural tissue - has the potential to alleviate the suffering of a great many people that have damaged nerves and/or brains)
But we all know how we judge morals in practice. Things that can complain get preference. Brains in jars won't complain. Nobody will ever make a picture of them showing big eyes behind bars. There will never be a scream or panic reaction available in full-color video of them. So they'll be abused, even tortured, even for very little gain. Because that's how humans judge morality ... in practice. If you believe otherwise, good luck explaining the morality of abortion.