With the recent change from Lightning to USB-C, it is likely that third-party manufacturers will be doing everything possible to avoid using Lightning.
To use Lightning, legally, the interface is licenced for the [Apple Approved] product - and then for every individual device manufactured with the Lightning connector an additional royalty fee is paid.
Back to the OPs question - whilst ignoring the cost of licences/royalties, it might be worth considering the technical complexities of why such an interface device is unlikely to ever be developed...
The 2018 iPad Pro has an industry standard USB-C interface that also supports USB PD. To adapt this interface to a Lightning connector, an active USB-C/Lightning interface-converter must be placed in-line, to perform both electrical and protocol conversion, prior to the physical Lightning connector pins. Connected to this additional Lightning connector will be another Lightning device (and active interface) that intercepts digital audio - and via a DAC produces analogue audio:
USB-C <-> Interface Converter <-> Lightning Connector (F) <<-> Lightning Connector (M) <-> DAC/Analogue Amp <-> EarBud
Compare this to the much simpler “supported” configuration:
USB-C <-> Interface Converter/DAC/Analogue Amp <-> EarBud
I’m not suggesting that it will never happen, but given the cost and unnecessary/avoidable complexity for a potentially tiny customer pool, a manufacturer is unlikely to see any return on the design, tooling and firmware development costs.