Is there Limitation of irule "virtual".. can we do it like this?

yep, this is a common scenario and works great. I'm not sure about a top-end limitation, you'd need to test. But with the iRule, if there more than a handful of hosts/policies, I'd recommend a data-group to map host header->virtual so you can keep the iRule logic light. Something like:

when HTTP_REQUEST {
  set vip_target [class match -value -- [HTTP::host] equals host2vipmap_dg]
  if {$vip_target ne ""} {
    virtual $vip_target
  } else { reject }
}

 with a data-group set up like:

ltm data-group internal host2vipmap_dg {
    records {
        abc.example.com {
            data VS_abc.example.com
        }
    }
    type string
}