Calling relocate on a fable transforms it into tsibble

> tsibble(quantity = dist_normal(1, 1:6), outlook = 1:6, index = "outlook") %>% as_fable(response = "quantity", distribution = "quantity")

# A fable: 6 x 2 [1]
  quantity outlook
    <dist>   <int>
1  N(1, 1)       1
2  N(1, 4)       2
3  N(1, 9)       3
4 N(1, 16)       4
5 N(1, 25)       5
6 N(1, 36)       6

after relocate

> tsibble(quantity = dist_normal(1, 1:6), outlook = 1:6, index = "outlook") %>% as_fable(response = "quantity", distribution = "quantity") %>% relocate(outlook)

# A tsibble: 6 x 2 [1]
  outlook quantity
    <int>   <dist>
1       1  N(1, 1)
2       2  N(1, 4)
3       3  N(1, 9)
4       4 N(1, 16)
5       5 N(1, 25)
6       6 N(1, 36)

Since relocate does nothing to the data in the table and I think it's only for presentation purposes, we should not lose the class.