Migrate 2.79 scenes - Step 1.py

import bpy
from bpy.props import *

# New texture slot class
class LegacyTextureSlot(bpy.types.PropertyGroup):
    texture = PointerProperty(type=bpy.types.Texture)
    name = StringProperty(name="Name", description="Name for this texture slot")
    uv_layer = StringProperty(name="UV Slot")
    
bpy.utils.register_class(LegacyTextureSlot)

# Define new material slot properties (used in 2.8x addon)
bpy.types.Material.th_texture_slots = CollectionProperty(type=LegacyTextureSlot)
bpy.types.Material.th_texture_slot_index = IntProperty(default=-1)

# Copy data from BI texture slots into new properties
for mat in bpy.data.materials:
    for tex_slot in mat.texture_slots:
        if tex_slot == None or not tex_slot.use: continue
        new_texslot = mat.th_texture_slots.add()
        new_texslot.uv_layer = tex_slot.uv_layer
        new_texslot.name = tex_slot.name
        new_texslot.texture = tex_slot.texture
        

Migrate 2.79 scenes - Step 2.py

import bpy
import bmesh
import io_thps_scene.material

# Move the 'alpha' vertex color values to the actual alpha channel in 'color' 
bm = bmesh.new()

meshes = [o for o in bpy.data.objects if o.type == 'MESH']
for ob in meshes:
    bm.clear()
    bm.from_mesh(ob.data)
    vc_layer = bm.loops.layers.color.get("color")
    bake_layer = bm.loops.layers.color.get("bake")
    alpha_layer = bm.loops.layers.color.get("alpha")
    
    if alpha_layer:
        # Create color layer if it none exist, or use the first layer
        if not vc_layer:
            if len(bm.loops.layers.color):
                #ob.data.vertex_colors[0].name = "color"
                #bm.loops.layers.color[0].name = "color"
                vc_layer = bm.loops.layers.color[0]
            else:
                vc_layer = bm.loops.layers.color.new("color")
        for face in bm.faces:
            for loop in face.loops:
                if bake_layer:
                    loop[bake_layer][3] = loop[alpha_layer][0]
                loop[vc_layer][3] = loop[alpha_layer][0]
        # Remove alpha layer
        bm.loops.layers.color.remove(alpha_layer)
        bm.to_mesh(ob.data)
bm.free()

# Finally, make sure shader nodes are generated for the materials
for mat in bpy.data.materials:
    io_thps_scene.material.update_node_tree(None, None, mat)
    
# Your scene should now be fully migrated to work with the 2.8x addon!