Switch for alternating between outlets
You are not allowed to put multiple outlets on a 50A/60A circuit.   You can on a 30A, and that would've been simple, but that will slow charge.

However, your Tesla charger wants 60A and you cannot put a 50A receptacle on a 60A circuit. 



Really, the best way to do this is a subpanel.  But wait.

The keystone is a $30 interlock kit made by Siemens for its panels.  This replaces the expensive, huge  Frankenstein switch. The interlock kit straps between two 2-pole breakers, making it so only one can be on at a time.  This is intended for generator interlocks, where the breakers are back-fed, but it's fine to normal-feed the breakers too.  So your cost is 


$30 interlock kit
$40 8-space, main-lug (no breaker on the sub**) panel 
$18 two 40-60A breakers, $9 each 
$5 ground bar


I also got you 4 extra spaces in the panel to use as you please. 

You feed the lugs normally, you don't backfeed. The two breakers on the interlock are 


a 60A breaker going to the Hardwired Tesla charger, full rate unthrottled
a 50A breaker going to the NEMA 14-50, which is the legal/right way to do that 


And honestly, I do not see a reason you can't simply forego the interlock and allow both outlets to be hot at the same time.  The breaker in the main panel protects the wiring to the subpanel and the subpanel itself (which is rated 125A), and the individual breakers protect the wiring to the equipment.  If you try to charge two cars at once without rate throttling, yeah, you'll trip the breaker downstairs.  

The feed from the main panel to this subpanel can be any size of wire you please, as long as the breaker in the main panel protects the wire.  At these sizes, there are no brownie points for using copper*, so consider aluminum wire/cable.  For 60A feeder, use #6Cu or #4Al.  For 100A feeder, #3Cu or #1Al at which point you definitely don't need the interlock. (You're allowed to oversubscribe a panel and this won't matter).

* Aluminum feeder does not have the problem that 1970s branch circuits had.  The metal conducts 12x better per dollar. This is why it is widely used on feeder, where the mineral value becomes a significant part of cable cost. 

** because it's not needed in subpanels in the same building, a breaker is needed in the main panel to feed/protect the cable run. Getting the subpanel main to pop before the feed breaker doesn't work, without deep-diving into SCADA tech.