The orphanage limits the "usage" of the orphans it stores, per peer and globally, to bound the amount of memory an attacker can make us hold on to. It uses weight as a proxy for that memory, on the assumption that weight is "often higher than the actual memory usage of the transaction".
That assumption does not hold for a deserialized transaction. Every witness stack element is an individually heap-allocated vector, costing its 24-byte slot in the stack vector plus a 32-byte minimum allocation, while only weighing 2WU. A transaction of 199,000 1-byte witness elements weighs 398,247WU (i.e. it is of standard weight, and witness standardness cannot be checked while the inputs are missing), but uses 11.1MB of memory: 28 times what is accounted for it, and one such orphan can be retained per peer.
Rather than change the accounting metric, keep orphans in serialized form, deserializing them again on the paths that hand them back out. Serialized, a transaction's memory usage is bounded by its weight, so the existing weight-based accounting becomes a true upper bound on memory and the worst case is the peers' combined allowances.
Admission, eviction and accounting behavior are unchanged: no transaction that was previously accepted is refused, so orphan resolution (and thus 1p1c package relay) keeps working for standard-weight transactions whose witnesses consist of many small elements, such as BitVM-style transactions.
