An incomplete Python3 module for Unbound 1.9.0 showing a proof-of-concept partial implementation of http://xip.io/ like functionality in Unbound, and an extension of the idea to support dynamic delegation (which I'm not sure is even a sensible thing to do).

module.py

import base64

# Based on: https://jpmens.net/2011/08/09/extending-unbound-with-python-module/

def init_standard(id, env):
    return True

def deinit(id):
    return True

def inform_super(id, qstate, superqstate, qdata):
    return True

def operate(id, event, qstate, qdata):
    if event == MODULE_EVENT_NEW or event == MODULE_EVENT_PASS:
        qdn = qstate.qinfo.qname_str.lower()

        if qdn.endswith(".asa.inet_aton.ximoneighteen.com."):
            # The xip.io-like case: respond with an A record.
            # Expects as input a dotted quad format IPv4 address sub-domain name.
            ipv4 = '.'.join(qstate.qinfo.qname_list[0:4])

            msg = DNSMessage(qdn, qstate.qinfo.qtype, qstate.qinfo.qclass, PKT_QR | PKT_AA)
            msg.answer.append("{} 300 IN A {}".format(qdn, ipv4))

            set_return_msg_and_finish(id, msg, qstate)

        elif qdn.endswith(".nsdel.inet_aton.ximoneighteen.com."):
            # A proposed 'xipdelegate.io' case: respond with NS and A glue records.
            # Expects as input a base 32 encoded dotted quad format IPv4 address which "points" to a
            # nameserver.
            b32 = ''.join(qstate.qinfo.qname_list[-6:-5])
            decoded = base64.b32decode(b32).decode('utf-8')

            msg = DNSMessage(qdn, qstate.qinfo.qtype, qstate.qinfo.qclass, PKT_QR)
            msg.authority.append("{}.isdel.inet_aton.ximoneighteen.com. 60 IN NS {}.asa.inet_aton.ximoneighteen.com".format(b32, decoded))
            msg.additional.append("{}.asa.inet_aton.ximoneighteen.com. 60 IN A {}".format(b32, decoded))

            set_return_msg_and_finish(id, msg, qstate)

        else:
            # Pass the query to validator
            qstate.ext_state[id] = MODULE_WAIT_MODULE

    elif event == MODULE_EVENT_MODDONE:
        qstate.ext_state[id] = MODULE_FINISHED

    else:
        qstate.ext_state[id] = MODULE_ERROR

    return True

def set_return_msg_and_finish(id, msg, qstate):
    qstate.return_rcode = RCODE_NOERROR

    # Set qstate.return_msg
    if not msg.set_return_msg(qstate):
        qstate.ext_state[id] = MODULE_ERROR
    else:
        # Indicate valid result
        qstate.return_msg.rep.security = 2
        qstate.ext_state[id] = MODULE_FINISHED