dmpopidor / app / views / plans / new.html.erb

<% if params[:v2] == "true" %>
<%= link_to 'Form v1', new_plan_path(v2: false) %>
<%= render "form_v2" %>
<% else %>
<%= link_to 'Form v2', new_plan_path(v2: true) %>
<%= render "form_v1" %>
<% end %>