Select next image in folder to replace smart object in batch recording.

Also be aware smart object layer have an associated transform.  This transform is not changed during the replace object content operation.  The replacement object must be the same size as the object being replaced for the associated transform to work correctly.

I think what you want to do could easily be done with one of the batch scripts I include in my package with out using a smart object layer in the template.  However the image will be place into the template as a transformed smart object layer.

Photo Collage Toolkit

Photoshop scripting is powerful and I believe this package demonstrates this A video showing a 5 image collage PSD template  being populates with images:

The package includes four simple rules to follow when making Photo Collage Template PSD files so they will be compatible with my Photoshop scripts.

1. Size the photo collage templates for the print size you want - width, height and print DPI resolution.
2. Photo collage templates must have a Photoshop background layer. The contents of this layer can be anything.
3. Photo collage templates must have alpha channels named "Image 1", "Image 2", ... "Image n".
4. Photo collage templates layers above the background layers must provide transparent areas to let the images that will be placed below them show through.

There are twelve scripts in this package they provide the following functions:

1. TestCollageTemplate.jsx - Used to test a Photo Collage Template while you are making it with Photoshop.
2. CollageTemplateBuilder.jsx - Can build Templates compatible with this toolkit's scripts.
3. LayerToAlphaChan.jsx - Used to convert a Prototype Image Layer stack into a template document.
4. InteractivePopulateCollage.jsx - Used to interactively populate Any Photo Collage template. Offers most user control inserting pictures and text.
5. ReplaceCollageImage.jsx - use to replace a populated collage image Smart Object layer with an other image correctly resized and positioned.
6. ChangeTextSize.jsx - This script can be used to change Image stamps text size when the size used by the populating did not work well.
7. PopulateCollageTemplate.jsx - Used to Automatically populate a Photo Collage template and leave the populated copy open in Photoshop.
8. BatchOneImageCollage.jsx - Used to Automatically Batch Populate Collage templates that only have one image inserted. The Collage or Image may be stamped with text.
9. BatchMultiImageCollage.jsx - Used to Automatically Batch Populate Any Photo Collage template with images in a source image folder. Easier to use than the interactive script. Saved collages can be tweaked.
10. BatchPicturePackage.jsx - Used to Automatically Batch Populate Any Photo Collage template with an image in a source image folder
11. PasteImageRoll.jsx - Paste Images into a document to be print on roll paper.
12. PCTpreferences.jsx - Edit This File to Customize Collage Populating scripts default setting and add your own Layer styles.

Documentation and Examples

I guess this needs proper Scripting and Actions are insufficient.

Replacing Smart Objects with a number of images in turn and saving copies from that has come up repeatedly so you may want to do a Forum search.