Bitcoin rises 6% on Monday to $48.2K as risk assets resurge and Citi considers the crypto asset at a "tipping point" between mainstream adoption or "speculative implosion."With Tesla's recent $1.5B investment in Bitcoin and companies like Mastercard and PayPal accepting payments, the crypto could be at the start of a "massive transformation" into the mainstream, Citi analysts said.If businesses and individuals get access through digital wallets to planned central bank digital currency and stablecoins, Bitcoin's global reach, traceability, and potential for quick payments would make it "optimally positioned" to be a preferred currency for international trade, they said.They still acknowledged that there are "host of risks and obstacles" to the everyday use of Bitcoin as a currency, they said.See why SA contributor Zvi Bar sees Bitcoin becoming a meaningful form of collateral.In premarket trading, Marathon Patent (MARA) jumps 16%, Riot Blockchain climbs 11%, and MicroStrategy (MSTR) gains 6.7%. Other tickers to watch: