@smedegaard As you have found out exporter_main_v2 is the script we recommend for exporting your model.
Also, all the meta arch (like SSD etc) inherit from a keras Layer. This may be of use to you
  

      github.com
  

  
    tensorflow/models/blob/master/research/object_detection/core/model.py#L71 2



      
      
          import abc
          import six
          import tensorflow.compat.v1 as tf
          
          
from object_detection.core import standard_fields as fields
          
          

          
# If using a new enough version of TensorFlow, detection models should be a
          # tf module or keras model for tracking.
          try:
            _BaseClass = tf.keras.layers.Layer
          except AttributeError:
            _BaseClass = object
          
          

          
class DetectionModel(six.with_metaclass(abc.ABCMeta, _BaseClass)):
            """Abstract base class for detection models.
          
          
  Extends tf.Module to guarantee variable tracking.
            """
          
      

    
  


  

  
    
    
  

  


Also note that an OD API model can be fine tuned using any of the checkpoints from model zoo, does that work for you ?
I was not aware of tf.saved_model.save being deprecated ? Can you send me a pointer to that ?
Unfortunately an object detection models will always have to output multiple values, but we can make some changes to the exporter if it can help your use case.
Thanks
Vighnesh