Please allow users/customers to create additional DS records for their zones even if they are using TransIP's authoritative nameservers.
This is required to allow for a smooth migration (e.g.: without downtime) of DNS zones from your nameservers to the customer's own nameservers, since it can take up to 24h until such changes to the parent zone (usually the TLD) have propagated through the whole DNS system.
Since many server operators actually validate DNSSEC signatures these days, broken trust/signature chains for a zone result in all sorts of nasty things such as mailservers getting a SERVFAIL when trying to deliver emails to such a domain, causing "Undelivered mail to sender because the recipient's domain doesn't exist" errors on the sender's end.
Whilst we're at it, please also allow customers to create glue records even if they are not (yet) using their own nameservers, because this artificial limitation causes similar problems as the one mentioned above. The only reason I can partly work around that limitation is because I happen to have a pile of other domains lying around - but still, I'd prefer to be able to create glue records, verify that they have been created and their existence has propagated through the whole DNS chain (think cacheing servers ignoring the TTL and similar things) before I actually flip the switch on my NS records.