Add testfor entity to block predicate

I dream of adding testfor entity to block predicate, because it makes judging whether a block is a special block (who has a entity marker with) possible.

This is a example: 

{
  "type": "minecraft:item",
    "conditions": [
      {
        "condition": "minecraft:survives_explosion"
      },{
        "condition": "if_entity",
        "at": "this",
        "selector": "@e[type=marker]"
      },
    ],
  "name": "minecraft:cobblestone"
}