In summary, it will be a L2 that works and feels like our experience in L1 without losing your privacy and at speeds as high as in the LN... Meaning, no liquidity constrains, not opening and closing channels, no balancing channels, LN is a mess, IMO it was doom, now that Phoenix came with a change adding to the LN wallets "splicing" (Splicing allows for resizing channels, eliminating the need for multiple channels per user) which means, a third generation wallet that will allow newbies and non tech people to have their wallet and just use it without any additional steps and/or worries, healthy competition is ON now, between LN with the Phoenix wallet splicing (in beta now) and what #ARK will bring to the equation. and yes, #ARK is self custodial, as it is Phoenix Wallet currently (a bit expensive, but worth it) and it will be the new version of Phoenix, much less expensive and self custodial as well.

This article does a good job explaining #ark:

https://bitcoinmagazine.com/technical/bitcoin-developer-introduces-new-layer-2-protocol-ark