The batch of 250 coming up will be US stocks, and we do not provide US ETFs for the reason @Viktor mentions above. There is a section about US ETFs in the announcement:
US ETFs. We can’t add ETFs which are listed only on US exchanges, as they do not publish a KID (key information document) which is currently a legal requirement in the UK.
Dan’s post above is in the context of UK and European fractionals, which will be both for stocks and ETFs.