If they were going to enter, they wouldn't manufacture it in the EU anyway. It's far too expensive. It would be a case of improving Purex and leveraging its brand and distribution channels.
They could also introduce the Persil brand via Purex too e.g. Purex PERSIL as a premium HE product.
However, the laundry detergent market's viciously cut throat and difficult to get any foothold in.
Even within Europe, Henkel has almost zero presence in the laundry market in the UK and Ireland, other than Filetti, an extremely minority detergent aimed at sensitive skin / baby care. They have no main stream presence here at all in that market. Effectively, other than store brands, Unilever and P&G have a near total duopoly.
However, if Henkel could use PERSIL technology to increase Purex's market share, that might be something they would persue. Particularly as there's a massive growing market for HE detergents and they would have no R&D costs. Just a matter of tweaking Dial Corp's plant to produce Persil.