Omit keys means module default (indirect)

Terraform
1

To allow omitting keys in live configuration means using module deafult values, I use a workaround like this (this example is for ebs, can be generalized):

(in module variables.tf)

variable "ebs_conf_defaults" {
  description = "EBS default configuration (override default inside live configuration)"
  type        = object({
    availability_zone = string
    type        = string
    size        = number
    encrypted   = bool
    kms_key_id  = string
    multi_attach_enabled = bool
    snapshot_id = string
    outpost_arn = string
    iops        = number
    tags        = map(string)
  })
  default     = {
    availability_zone = ""
    type        = "st1"
    size        = 0
    encrypted   = false
    kms_key_id  = ""
    multi_attach_enabled = false
    snapshot_id = ""
    outpost_arn = ""
    iops        = 0
    tags        = {}
  }
}
variable "ebs_conf" {
  description = "EBS configuration (with ebs_conf_defaults to allow default/optional values, see merge in main locals)"
}

(in module main.tf)

###     Local definitions
locals {
  merged_ebs_conf = merge(var.ebs_conf_defaults, var.ebs_conf)
}

availability_zone    = local.merged_ebs_conf.availability_zone
...

(in live config)

locals {
  ebs = {
    "ebs1" = {
      "create" = true
      "availability_zone" = "${local.region1}a"
     "type" = "gp2"
      "size" = 8
      "tags" = {
        "Environment" = "${local.env_prefix}${local.env}"
      }
    }
    "ebs2" = {
      ...
    }
  }
}

module "ebs" {
  source = "..."

  for_each = {
    for key, value in local.ebs:
    key => value
    if value.create
  }

  ebs_conf = each.value
}

So i can decouple module upgrade (support for new keys/funcionalities) from live configurations (backwards compatibility) and also allow management o live configuration driven by locals data structures centralized and simple to manage.

This solution works great, but has a limit imposing module specific configuration so I cannot use in live configurations this omit means use module default values logic with e.g standard modules written by other (with separated single variables definition).

There is a solution to keep both benefits ?