I generally agree, interactive txs are not a big issue in most cases, but I see two cases where interactive transactions cannot be used in a secure way (both previously discussed in the forum), which means that they cannot be used at all under some circumstances:
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Checkout for ecommerce. These systems need to automatically provide an invoice to the customer. Grin can create invoices, but they need to be signed with a hot key, which means an online shop would be required to keep its hot wallet online, which is not secure.
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Donations. This is a similar case, but the sender would initiate the transaction. In order to automatically countersign an incoming transaction, the receiver, again, needs to keep its hot wallet online.
These are not UX issues, but things that can only be solved at protocol level as far as I can tell.