Thanks for writing a clear and succinct draft. I only found one issue of note, around the registration of the new udpOptions Information Element.

Section 4.1:
The data type used for the “udpOptions” entry is just listed as “unsigned”, and is described as being either an unsigned32 or an unsigned64. However, when I look at the registry at https://www.iana.org/assignments/ipfix/ipfix.xhtml, I don’t see any entries that use this abstract “unsigned” type, and it is not listed as an option in the element data types. Is there a reason this shouldn’t just be registered as an unsigned64? My understanding from https://www.rfc-editor.org/rfc/rfc7011#section-6.2 is that an unsigned64 can be automatically encoded as an unsigned32 if the value is small enough, so the definition can just use unsigned64.